EMC CLARiiON Backup Storage Solutions

Transcription

1 Engineering White Paper Backup-to-Disk Guide with VERITAS NetBackup Abstract This white paper describes how to configure the EMC CLARiiON CX200, CX400, and CX600 storage systems with VERITAS NetBackup for best performance as destinations for backups. It also compares the benefits and performance characteristics of backup-to-disk versus backup-to-tape implementations. Published 3/3/2003

2 Copyright 2003 EMC Corporation. All rights reserved. EMC believes the information in this publication is accurate as of its publication date. The information is subject to change without notice. THE INFORMATION IN THIS PUBLICATION IS PROVIDED AS IS. EMC CORPORATION MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WITH RESPECT TO THE INFORMATION IN THIS PUBLICATION, AND SPECIFICALLY DISCLAIMS IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Use, copying, and distribution of any EMC software described in this publication requires an applicable software license. Part Number H867.1 Backup-to-Disk Guide with VERITAS NetBackup 2

3 Table of Contents Summary...4 Introduction...4 Disk Backup Overview...5 Advantages of Backup-to-Disk... 5 Backup Performance... 5 Restore Performance... 6 Media Reliability and Data Availability... 6 Overall IT Efficiency... 6 CLARiiON Backup-to-Disk Performance Factors...6 RAID Types... 7 Factors Affecting I/O Sizes... 7 File System Block Size... 7 Disk-Array Element Size... 7 CLARiiON Configuration Settings... 8 Disk-Array Cache Settings... 8 LUNs per RAID Group... 8 Recommendations for Disk-Based Backups... 8 Windows File System Tuning... 8 Solaris File System Tuning... 8 EMC CLARiiON Storage Arrays...9 ATA Technology... 9 VERITAS NetBackup...10 LAN-Free Backup and Recovery NetBackup Basic Architecture...11 Disk-Based Backup Configuration Backup Performance Analysis and Results...13 Dataset Description CLARiiON Raw Throughput Performance Overall Backup/Restore Time CLARiiON Storage Array versus Native Tape Drive Performance VERITAS NetBackup Performance Results...20 Backup and Restore Performance Results Conclusions...22 Appendix A: Tape Drive Characteristics...23 Appendix B: Related White Papers...24 Appendix C: Related Articles...25 Backup-to-Disk Guide with VERITAS NetBackup 3

4 Summary Storage backup solutions that incorporate backup-to-disk yield significant benefits over traditional backupto-tape. These benefits include: Near-term recovery of mission-critical data Rapid restore from disk Greater reliability of the backup medium Multiple host data streams to disk As a complement to using tape for long-term storage, backup-to-disk is an emerging and powerful solution for rapid recovery of mission-critical data. There are many applications that require frequent retrievals of recently captured data, as well as the pervasive need for backup of business crucial data that must be preserved and retrieved quickly and efficiently. Leading-edge customers are using disk as the destination for storage management application output. Advanced Technology-Attached (ATA) disk technology provides benefits over tape with the performance of disk. Backup arrays or disk-based backups will not replace tape, but will shift tape into an archival role. Today, EMC recommends adopting a backup-to-disk solution when performance and data reliability are the customer s primary concern. Introduction This technical white paper explains implementing backup-to-disk technology with VERITAS NetBackup and the many advantages over traditional backup-to-tape. This implementation has been tested and endorsed by EMC engineering. This document contains information relating to VERITAS NetBackup, and identifies what to expect from EMC CLARiiON storage systems when used as destinations of backups. It also compares the performance of CLARiiON storage systems to today s high-performance tape drives such as SDLT and LTO technologies. EMC s CLARiiON Application Solutions Integration and Performance Engineering teams performed tests using specific system configurations. Due to variations in hardware, software, disk layout, compressibility of data, system usage, and other factors, backup rates achieved in some situations may be different than those shown herein. All testing performed by the Applications Solutions Integration and Performance Engineering teams used the most up-to-date backup software available at that time. Other versions of these applications may yield other results. Backup-to-Disk Guide with VERITAS NetBackup 4

5 Disk Backup Overview Traditionally, backup software was created to write to a tape device. Today, most backup software products also support writing to disk, which means writing to a disk file in a file system. The file system may be on a Windows, NetWare, or UNIX platform, depending on the backup server. Disk-based RAID configurations enhance data protection beyond what tape can provide. With the CLARiiON CX series storage systems, backups to disk are equal to or faster than tape drives when comparing raw throughput performance. Backup and restore time using disk provides customers an advantage over using traditional tape. Disk drives are random access devices and can instantly start to transfer the files, whereas with tape, the tape must be loaded and then accessed, increasing the overall time. File system overhead and tape drives with on-board compression add more time lags. Under normal conditions, I/O will always go to physical disk. Performances are characterized by the physical disk rotational speed and seek time together with the file system characteristics. Using a larger file system block size or allocation unit size (cluster size) may improve performance of disk backups by using larger contiguous address space for files because the operating system allocates fewer groups of contiguous sectors. CLARiiON disk cache improves overall performance. Results show that running with write cache enabled will provide significantly better performance than when cache is turned off. The CLARiiON engineering team examined the effects of various CLARiiON settings on physical write and read rates prior to running the tests, so that these settings could be varied during the backup tests. Benefits of CLARiiON disk-based backups that are discussed in more detail in this white paper include: Random access characteristics of disk versus sequential access for tape Simultaneous capability to read/write to disk Multiple host data streams Disk performance compared to tape performance with compression Aggregate performance Raw disk performance Advantages of Backup-to-Disk Traditionally, tape has been the backup medium of choice, due to its cost-per-mb advantages compared with disk. However, the economics of disk are narrowing that gap. The advantages of using disk over tape with backup solutions can be grouped into four major categories: Backup performance Restore performance Media reliability and data availability Overall IT efficiency The following sections summarize these benefits. Backup Performance CLARiiON storage systems are much faster than the new-technology tape drives such as SDLT and LTO. Some tape technologies respond to a minimal data stream by shoe-shining or excessive positioning. Disks do not experience this behavior because they are inherently random access. Backup-to-Disk Guide with VERITAS NetBackup 5

6 Restore Performance Faster recovery time for disk drives over tape and tape drives. The difference can be seconds or minutes, versus hours with tape. Disks support random and sequential access. Tapes support sequential access only. This enables faster access of data files, improving overall performance. If data is on several tape cartridges, the following steps are required to restore the data: 1. Each tape must be mounted by the library (up to a minute per tape). 2. The tape must load (30 seconds to a few minutes). 3. The tape must be positioned to the desired data (an average access time is a few minutes). 4. The tape must be rewound and unloaded (30 seconds to a few minutes). 5. Load the next tape and repeat cycle. Time to first byte takes milliseconds for disk versus seconds to minutes for tape. Media Reliability and Data Availability Media-specific errors, including faulty tape media, are reduced. Disk system RAID protection prevents data unavailability or data loss in the event of a disk drive failure. Tape handling is reduced or eliminated. Maintaining a set of tapes from a tape library can be problematic and requires properly trained personnel. Overall IT Efficiency Disk does not require the tape handling/positioning and RAID protection makes it inherently more reliable. There is less need to perform frequent full backups. Fewer backups need to be performed, saving network and CPU load. Tape undergoes a technology shift every three years, so a conversion process from old to new media must be undertaken at that interval. Disk technology does not go through these types of transitions since the format of the data is not changed as it is with tape technology. New larger-capacity disk drives reduce floor space requirements compared with equivalent-capacity tape libraries. CLARiiON Backup-to-Disk Performance Factors This section describes the specific parameters that can be altered to improve performance of backup-todisk. EMC varied these to determine recommended settings for best performance when backing up to a disk file. In addition to using backup software to measure CLARiiON performance, EMC also used lower-level tests to measure performance. Backup solutions that use disk as a backup destination, write sequentially to the disk. The source data (data that is read for backup) can be located anywhere on the source. Backup bandwidth to disk can be directly impacted by the fragmentation of the source file system. Various backup packages write in particular block sizes. EMC tested sequential writes with block sizes of 32, 64, 128, and 256 KB. Note: EMC did not exhaustively test all the combinations of parameters. The number of permutations would be unrealistic to simulate. Backup-to-Disk Guide with VERITAS NetBackup 6

7 RAID Types CLARiiON storage system use RAID technology to combine disks into one logical unit (LU) to improve reliability and/or performance. CLARiiON supports five RAID types; RAID 5, RAID 3, RAID 1, RAID 0, RAID 1/0. RAID 0 is a simple stripe and a single drive failure will result in loss of data. The other RAID types offer high availability and data reliability. The storage system can read and write to multiple disks simultaneously and independently and allow several read/write heads to work on the same task at once. EMC recommends RAID 5 RAID groups. They offer excellent read performance and good write performance. Write performance benefits greatly from CLARiiON storage-system caching. RAID 5 configurations are very suitable as disk-backup devices. RAID 1 devices are limited in terms of storage capacity; therefore, they do not lend themselves to backupto-disk solutions. RAID 1/0 devices offer both data availability and storage capacity but at a cost. This RAID configuration requires twice the number of disk drives, which increases the backup storage cost. RAID 3 devices are designed for bandwidth applications that are characterized as very large I/O, 1 MB in size and larger. Backup I/O sizes are typically smaller than this. A RAID 3 device cannot take advantage of the CLARiiON storage-system cache. RAID 5 configurations are very suitable as disk-backup devices. Destination backup devices are written to in a sequential pattern. The optimizations in FLARE for RAID 5 devices are a perfect fit for this type of application. The write requests are written to the write cache on the storage system and mirrored in the second storage processor write cache. FLARE then destages this data to disk in an MR3 manner. Factors Affecting I/O Sizes The following two factors affect I/O sizes: File system block size Disk-array element size The following sections describe each of these factors. File System Block Size Operating systems allocate space for files in blocks. The file system block size varies depending on the OS being used. A larger file system block size provides a large I/O size, which can increase the bandwidth of a backup. Larger block sizes may reduce file system fragmentation. The fragmentation of a file system can also impact the backup bandwidth. The source file system (the file system being read for backup) should be as defragmented as possible. This helps the backup utility to perform read requests more sequentially. The default file system block size for UFS, the native Solaris file system, is 8 KB. UFS can be configured with either 4 KB or 8 KB. EMC recommends that the defaults be used. Note: The disk defrag tool included in Windows 2000, will not work with cluster sizes greater than the default cluster size of 4 KB. Disk-Array Element Size The element size of a RAID device is defined as some number of 512-byte sectors. The element size defines the RAID group's stripe size and this can have an impact on the behavior and therefore performance of a RAID device. The default element size for a RAID 5 device is 128, which is 64 KB. A five-drive RAID device has a stripe size of 256 KB. Algorithms in FLARE try to optimize back-end writes to a RAID 5 device. This type of optimized back-end I/O is termed MR3 writes. EMC recommends using the default RAID 5 element size for devices that will be used for backup-to-disk devices. Backup-to-Disk Guide with VERITAS NetBackup 7

8 CLARiiON Configuration Settings This section describes the CLARiiON-specific parameters that can be altered to improve backup-to-disk performance. Disk-Array Cache Settings CLARiiON storage-system caching improves read and write performance for several types of RAID groups. Read and write caching improve performance in two ways: For a read request, the array senses sequential reads from the host, and then starts to prefetch data from the back end into the read cache. The host then reads the data from cache. For a write request: SIncoming host write requests are written to cache and then mirrored to the second storage processor. The host request is then acknowledged. Writing the data to the cache allows for a faster response time. SIf the request modifies the same page in the write cache that has not yet been written to disk, the storage system updates the information in the cache before writing it to disk. One might anticipate that turning off the CLARiiON storage-system cache would benefit backups. However, EMC found a counter-intuitive result: Performance with the cache off was reduced, even when the writes were aligned on the proper boundaries (such as 256 KB). EMC found minor effects on performance when varying the amount of memory dedicated to write cache. Similarly, little impact was noticed when varying the high and low watermarks. LUNs per RAID Group EMC recommends only using one LUN per RAID group for disk-based backup applications. Multiple LUNs are not recommended because concurrent I/O would cause the underlying physical disks to seek between the sectors used by the various LUNs, thereby deteriorating performance. Recommendations for Disk-Based Backups Consider the following disk-based backup guidelines when planning your CLARiiON configuration: Use a five-disk RAID 5 configuration. Use write cache. In some circumstances, having the write cache enabled will allow misaligned data to be written out as a hardware stripe (written as MR3). RAID 1/0 will give better performance than RAID 5 if boundaries are aligned. Windows File System Tuning Windows systems create a 63-sector hidden area on disk to house the Master Boot Record (MBR). This causes all I/O in the file system made on the subsequent partition to be misaligned (not on a 256 KB boundary), and therefore I/O performance will suffer. By using a program called diskpar, available on the Windows 2000 Resource Kit, you can alter the number of hidden blocks to a larger number so that the disk array I/Os are aligned and better optimized. Note: The disk defrag tool included in Windows 2000 will not work with cluster sizes greater than the default cluster size of 4 KB. Solaris File System Tuning There are two possible values to tune with Solaris. The first is to ensure that maxcontig for the file system in question is set high enough; otherwise, rotational delays will be incurred when laying down all the sectors in the write. Set maxcontig to the maximum number of sectors in a write. Since it may be Backup-to-Disk Guide with VERITAS NetBackup 8

9 3/3/2003 difficult to know exactly what the backup software will use, EMC recommends setting maxcontig to 256 (equivalent to 128 KB since there are 512 bytes in a sector). The maxcontig value may be set when making a file system (such as with newfs) or later with tunefs. The second value is the maximum number of bytes that can be written out in a single I/O. This value is by default 128 KB or 256 KB, depending on the hardware on which Solaris is running. There is little reason to go to 256 KB because the backup software would have to change to take advantage of the larger I/O size. For completeness, this line may be added to allow 1 MB I/O: set maxphys= EMC CLARiiON Storage Arrays CLARiiON storage systems provide leading performance scalability and investment protection. These storage solutions feature modular building blocks, based on advanced sixth-generation Fibre Channel technology. EMC Fibre Channel CX series disk-array storage systems provide terabytes of disk storage capacity, high transfer rates, flexible configurations, and highly available data at affordable price points. Hardware RAID features are provided by two storage processors (SPs). There are three members of the CLARiiON CX series storage-system family: CX600, CX400, and CX200. Figure 1. CLARiiON CX Series Overview ATA Technology EMC has implemented ATA disk technology with CLARiiON. This enables customers to keep more data online for longer periods of time. For many, previous alternatives were not affordable or justifiable. Customers can now mix and match performance Fibre Channel drives and capacity ATA drives within the same array, under common management. The CLARiiON software suite supports ATA drives. This singlearray implementation provides the deployment flexibility customers seek. Backup-to-Disk Guide with VERITAS NetBackup 9

10 To optimize CLARiiON storage systems for a backup-to-disk configuration, follow the guidelines in Table 1. Table 1. CLARiiON Disk-Based Configuration Guidelines CLARiiON System Page Read Cache Write Watermark Size SP-A SP-B Cache Low High CX KB CX KB CX KB * Cache values are in MB VERITAS NetBackup VERITAS NetBackup is an enterprise data management product that provides backup, archiving, and recovery services for UNIX, Windows NT, Windows 2000, and PC client systems in client/server networks. It can be scaled to serve any size operation ranging from a stand-alone system to an entire enterprise. VERITAS NetBackup provides media management, disaster recovery support, and Java and Windows administrative interfaces. In addition to protecting data in a mixed UNIX, Windows NT, Windows 2000, and Novell NetWare environment, VERITAS provides application-aware solutions for all leading applications including Oracle, Informix, Sybase, DB2, SAP R/2, NCR Teradata, Microsoft SQL Server, Microsoft Exchange, and Lotus Notes. NetBackup offer the following capabilities on a Fibre Channel SAN: LAN-free backup and recovery Tape drives and libraries shared between multiple servers EMC CLARiiON IP4700 File Server backup and recovery LAN-Free Backup and Recovery Traditional enterprise backup solutions required the use of the company s LAN for backup and recovery traffic. The impact of large backup and recovery operations including degraded server and LAN performance resulted in lost productivity. VERITAS NetBackup provides a solution for LAN-free backup and recovery that moves these operations off the LANs and onto SANs entirely. VERITAS NetBackup DataCenter can be used in a SAN environment with the following benefits: Reduced LAN traffic: With NetBackup, you can move backup traffic off of the production LAN and put it onto the SAN. All NetBackup Media Servers have access to backup devices over the SAN, which enables parallelism to decrease backup time. Centralized control: One NetBackup Master Server can control many NetBackup Media Servers and clients. With NetBackup Global Data Manager (GDM), you can control many Master Servers from a single console. Cross-platform administration: The administration interface remains the same whether on a UNIX or Windows machine. Adding Global Data Manager to this allows administrators to manage data from anywhere. The Java-based console can reside on UNIX or Windows platforms, managing NetBackup DataCenter, NetBackup Business Server, and Backup Exec systems running within UNIX, Windows, or NetWare environments. Backup-to-Disk Guide with VERITAS NetBackup 10

11 Disaster recovery: Disasters do not always allow a restore to the original source host. NetBackupdirected restore allows you to specify the host to restore to, as long as the new host has the same operating system as the original host. NetBackup Basic Architecture VERITAS NetBackup is based on a client/server architecture. Each NetBackup client and server belongs to a storage domain. A storage domain consists of a single Master Server, its associated Media Servers, and NetBackup clients. The Master Server controls and directs all NetBackup operations in its storage domain. Each Media Server controls the backup devices it is connected to, including direct-attach and SAN devices. A Media Server can have only one Master Server, but a Master Server can control more than one Media Server. The NetBackup clients are any systems containing data to be backed up. A Master Server can act as a Media Server, and both are capable of being clients. A NetBackup client is any system with data to be backed up. The client software is tailored to the operating system on which it is installed. Normally, a client operates under the control of the Master Server according to the rules and schedules that an administrator establishes. A backup client accesses the storage media through a Media Server. A NetBackup Media Server hosts one or more backup devices (tape or other storage media). Storage devices on the same SAN can be shared between Media Servers using the Shared Storage Option (SSO). The Master Server directs a client to send its data to a Media Server for backup. A NetBackup Master Server is the manager of the storage domain. An administrator can control all NetBackup functions in the storage domain from the Master Server. NetBackup manages client data in increments called backup images. A backup image originates from a single client and may consist of a file, a directory, a file system, a partition, or a database. The NetBackup file database on the Master Server contains detailed information about each backup image such as the filename of each file stored, time of backup, size, permissions, ownership, etc. An entry for each backup image is also written in the Master Server's volume database, which maps the backup images to the volumes where they are stored, stores the browse and retention policies for each save set, and maintains tracking information for all storage volumes. The file database and volume database are essential to NetBackup s ability to locate and recover data rapidly. Disk-Based Backup Configuration NetBackup can back up to disk as well as to tape. To prepare NetBackup for disk-based backup operation, you must configure it via NetBackup Management s Storage Units screen. To do so, follow these steps: 1. Right-click and select New Storage Unit. 2. In General Properties under Storage unit type, select Disk as shown next. Backup-to-Disk Guide with VERITAS NetBackup 11

12 Figure 2. VERITAS NetBackup Add New Storage Unit Screen 3. Click Storage Unit Type Properties and enter the information. The following is an example. Figure 3. VERITAS NetBackup Storage Unit Type Properties Screen Backup-to-Disk Guide with VERITAS NetBackup 12

13 To verify and configure backup jobs, select Policies from the NetBackup Management screen. Figure 4. VERITAS NetBackup Policies Screen Here you would select the policy storage unit, in this case the CX400, and select the files to be backed up along with other configuration settings. Default settings for disk-based backup and restore operations are below average. You can change several settings to improve performance. In particular, changing the Size_Data_Buffers setting improved performance. The default value is 64 KB. EMC increased the setting to 256 KB and 512 KB. The value tested and reported in the performance charts was 256 KB. For instructions on how to change this and other parameters, refer to the VERITAS NetBackup Performance Tuning on Windows guide. Note: SIZE_DATA_BUFFERS contains a single integer telling NBU the size of the shared data buffer in bytes. These buffers are temporary staging areas of the data and they directly affect the throughput of backup and restore. Default is 64 KB (65536 bytes). You can tune this value if you are backing up to RAID storage to take advantage of the multiple disks. Backup Performance Analysis and Results Customers who are considering moving to a backup-to-disk implementation are usually meeting their backup windows today. To be effective, backup-to-disk needs to be comparable to tape backup in all operational aspects including performance, overall completion time, and reliability. However, the adoption of backup-to-disk will not be driven by improvements in backup performance alone. The combination of affordable price points with the improved performance and reliability creates a compelling business proposition. A subset or single file restore from disk will provide a sizable improvement compared to restoring the file from tape. Disk-based implementations provide the random access characteristic of a disk drive when performing a restore task. With tape-based backups, you must also account for the library media load time, Backup-to-Disk Guide with VERITAS NetBackup 13

14 tape ready, seek time, etc. These can add several minutes to hours, in most cases, to the overall time it takes to complete, depending on the size of the restore operation. The following charts show the various backup and restore results for the combinations of CLARiiON storage systems, tape drives, and configuration environments that were tested. In most cases, the Y-axis shows megabytes per second (MB/s) and the X-axis shows the file set used to back up and restore, unless otherwise noted. Dataset Description Large dataset (each directory is 2 GB) S1 GB size files 2 files S100 MB size files 20 files S10 MB size files 200 files S1 MB size files 2,000 files Small dataset (directory is 503 MB) S50 KB size files 10,000 files Each CLARiiON storage system was configured with three RAID groups (RAID groups 0-2). Raid group 0 was placed on SP-A (storage processor), and RAID groups 1 and 2 were placed on SP-B, all in a RAID 5 configuration. RAID groups 0 and 1 (FC disks) were configured with five disks, and RAID group 2 (serial- ATA disks) was configured with nine disks. In a Microsoft Windows system, each LUN had its own drive letter. On a Sun Solaris, there was a mount point for each one. One dataset had a representative 2:1 compression ratio; the other had a 3:1 compression ratio. If there were no impediments reading the data from disk, and if the backup software was efficient writing to the destination device, throughputs to the tape devices would be double the native transfer rate when using the 2:1 dataset. That implies backup rates of 22 MB/s to SDLT 220, 30 MB/s to LTO, and 32 MB/s to SDLT 320 (since the native or uncompressed transfer rates are 11, 15, and 16 MB/s, respectively). Compressibility of data does not affect the rate at which backups can be done to disk; only tape drives have internal hardware compression. When data cannot be compressed,, tape drives would be limited to their native transfer rates. Some file types that are already compressed include video and music files, pictures, zip files, and some database applications to name just a few. In these scenarios, backup-to-disk performance compares even more favorably to tape than it does with compressible data. Aggregate Performance Total aggregate performance will vary depending on the type of CLARiiON storage system used, the type of backup host, file system, and nature of the data. Expect a maximum per LUN throughput of 40 MB/s to 60 MB/s when only one or two LUNs are active. As more and more backup streams (LUNs) become active, the total aggregate throughput will increase. CLARiiON Raw Throughput Performance The CLARiiON storage arrays were tested for raw performance in read and copy operations. The purpose of the read test was to see how fast the data could be read from one LUN. The copy operation tested the CLARiiON storage array for how fast it can read data from one LUN and write it to another LUN on separate RAID groups (and SPs). The following chart shows the results of these tests with the CX600, CX400, and CX200 storage arrays using both Fibre Channel disks (five disks) and serial-ata disks (nine disks). Backup-to-Disk Guide with VERITAS NetBackup 14

15 CLARiiON Raw Performance Throughput MB/s CX600 FC CX600 ATA CX400 FC CX400 ATA CX200 FC 10 0 Read Copy Figure 5. CLARiiON Raw Performance Throughput Results Testing Environment CX200 CX400 CX600 Sun Solaris Enterprise 250 EMC DS-16B2 FC Switches Dell PE-2550 Windows 2000 CrossRoads 10K FC to SCSI Bridge SDLT 320 Tape drive SDLT 220 Tape drive HP LTO Dell PV-132T IBM LTO Internal FC Bridge Tape drive Figure 6. Backup-to-Disk SAN Testing Configuration Diagram Backup-to-Disk Guide with VERITAS NetBackup 15

16 Overall Backup/Restore Time When comparing the performance of a backup-to-disk implementation to a backup-to-tape implementation, you must consider both the throughput performance and the overall time it takes to complete a backup or restore. This section explains the vast difference in overall time it takes to perform a backup or restore task. In a backup scenario comparing backing up to disk versus backing up to tape, different steps are required to accomplish the job (2 GB in size). A brief description of each task is described along with the average time to complete. In a backup-to-disk scenario, the following steps are involved: Upon request, data starts to be transferred from the source (disk) to the destination (disk) (typically less than five seconds depending on backup application to start the transfer). Once the dataset has been backed up, the backup application can immediately start the next task. Disk-to-Disk Backup Time Total Elapsed Time :55 4% 96% File Access Time Xfer Data Figure 7. Overall Disk-to-Disk Backup Time The advantage of disk-based backups is the random access characteristic of disk drives along with their speed and (in the case of the CLARiiON storage arrays) data protections with RAID protection and redundancy protection. The overall time it took to back up a 2 GB dataset to disk was 55 seconds; the backup-to-tape took 3 minutes, 50 seconds. In a backup-to-tape scenario, the following example illustrates the steps are involved: 1. Load a tape cartridge into a tape drive (10 seconds). 2. Wait for the drive to load the tape and become ready (15 seconds; up to 1 minute or more for a new tape media). 3. Tape drive must position the media to where the data will be written (up to 70 seconds or more). 4. Back up the data to tape (performance is determined by a variety of factors) 1. 1 Having a fast tape drive doesn t ensure the highest throughput. If the transfer rate of a tape drive is faster than the host data rate, the tape must stop and reposition frequently, degrading performance. Backup-to-Disk Guide with VERITAS NetBackup 16

17 The data could need more than one tape media to complete the backup. 5. Unload tape from drive (up to 70 seconds depending on position of tape). 6. Repeat the cycle for each tape that is required. Disk-to-Tape Backup Time Total Elapsed Time 3:50 2 GB Dataset 4% 7% 31% 30% 28% Tape Load Tape Ready File Access Time Xfer Data Rewind/Unload Figure 8. Overall Disk-to-Tape Backup Time Only 28 percent of the overall time is actually transferring data to tape, the other 72 percent is tape mechanical movement, file access time, and other tasks. There is extensive overhead associated with backup-to-tape. Most applications will stop a backup job if a restore job is submitted. This means unloading the tape in the drive and loading the restore tape. When the restore job is finished, the backup job will continue. With disk-based configurations, both jobs can run simultaneously. This section explains the differences in overall time to perform a restore of a typical dataset in a backup-todisk scenario versus a tape restore. This example illustrates a typical scenario where a full backup was performed on one day followed by a daily incremental backup, and a subset of the data is to be restored. In a disk-to-disk restore scenario, the following steps are performed: 1. Upon request, data starts to be restored from the full backup set to the destination site (typically less than five seconds depending on backup application). 2. Once the full dataset has been restored, the first incremental dataset starts to restore, in most cases immediately. 3. The second incremental dataset starts once the first incremental dataset is completed. 4. Data is restored with no additional overhead time, as is the case with tape. Backup-to-Disk Guide with VERITAS NetBackup 17

18 Disk-to-Disk Restore Time Total Elapsed Time : GB Dataset Full Backup + Two Incremental 4% 96% File Access Time Xfer Data Figure 9. Overall Disk-to-Disk Restore Time In the tape restore scenario, the following steps are needed to restore the data that may be scattered on several tapes: 1. Load the full backup tape into the drive (10 seconds). 2. Allow time for the drive to load the tape and become ready (15 seconds). 3. Wait for the tape drive to position the media to where the data resides (up to 70 seconds or more). 4. Restore the data to disk (performance is determined by a variety of factors) 2. The data could be on more than one tape that will add to more overhead time. 5. Unload tape from drive (up to 70 seconds depending on position of tape). 6. Load the first incremental tape into a drive (up to 10 seconds). 7. Wait for the drive to load the tape and become ready (15 seconds). 8. Allow the tape drive to seek to where the data resides (up to 70 seconds or more). 9. Restore the data to disk Unload tape from drive (up to 70 seconds). 11. Load the second incremental tape into a drive (10 seconds). 12. Wait for the drive to load the tape and become ready (15 seconds). 13. Allow the tape drive to seek to where the data resides (up to 70 seconds or more). 14. Restore the data to disk. 2 Performance of any tape device with hardware compression depends on the compressibility of the data to achieve maximum performance of the tape drive; otherwise, performance will suffer. Backup-to-Disk Guide with VERITAS NetBackup 18

19 Data is restored. If files to be restored are not sequential on tape, you will need to add more time for file seeks on the tape media. Tape-to-Disk Restore Time Total Elapsed Time 12: GB Dataset Full Backup + Two Incremental 4% 6% 45% 37% 8% Tape Load Tape Ready File Access Time Xfer Data Rewind/Unload Figure 10.Overall Tape-to-Disk Restore Time These examples show a typical scenario where a subset of data is requested for restoration. As the chart shows, it took the disk-to-disk restore about 45 seconds to restore the data (1.5 GB). In the tape-to-disk scenario, it took roughly 12 minutes, 45 seconds to complete. This example also accounts for the fact that the requested data can be located on several incremental backup sets or media that all must be loaded and unloaded. Users should account for this overhead when comparing performance of restore media. Customers should consider their recovery time objective, reliability needs, and footprint requirements when determining their optimal solution. Backup-to-Disk Guide with VERITAS NetBackup 19

20 CLARiiON Storage Array versus Native Tape Drive Performance The following chart shows performance results while backing up a dataset that is either already compressed or where the tape drives have compression turned off. CLARiiON vs. Native Tape Drive Performance MB/Sec CX600 FC CX600 ATA CX400 FC CX400 ATA CX200 FC SDLT 320 LTOs SDLT Figure 11. CLARiiON versus Native Tape Drive Performance with VERITAS NetBackup The CLARiiON storage arrays perform two to four times faster than tape drives when the dataset is not compressible or tape drive hardware compression is turned off. Tape drives can compress data in hardware and achieve better performance. Backup software packages can compress through software. EMC found that performance suffered significantly when enabling this option, and EMC does not recommend using software compression unless customers are trying to conserve disk space. VERITAS NetBackup Performance Results The following charts compare the performance of backing up to disk versus backing up to tape. The charts only show raw throughput of each device while data is being transferred and do not take into account tape positioning, file seek times, or library mechanical load/unload times. Backup-to-Disk Guide with VERITAS NetBackup 20

21 Backup and Restore Performance Results The following charts show the performance results while backing up a dataset that is either already compressed or where the tape drives have compression turned off. VERITAS NetBackup Backup Performance Data 40 MB/Sec CX600 CX400 CX200 SDLT320 LTO SDLT220 0 Disk-to-Disk FC-to-FC Disk-to-Disk FC-to-ATA D-to-T FC-to-Tape Figure 12. Backup Performance Results VERITAS NetBackup Restore Performance Data 50 MB/Sec CX600 CX400 CX200 SDLT320 LTO SDLT220 0 Disk-to-Disk FC-to-FC Disk-to-Disk FC-to-ATA D-to-T FC-to-Tape Figure 13. Restore Performance Results Backup-to-Disk Guide with VERITAS NetBackup 21

22 Conclusions Backup-to-disk is emerging as a technology that offers significant benefits over the traditional tape backup process. With the changing economics of disk technology, backup-to-disk solutions are now affordable. Leading-edge customers are implementing backup-to-disk solutions as improvements to their existing tape implementations. VERITAS NetBackup offers the backup-to-disk functionality. It leverages the superior performance of CLARiiON storage systems. EMC engineering has tested and supports VERITAS NetBackup with CLARiiON CX series arrays. Major advantages of backup-to-disk include: Backup performance Restore performance Media reliability and data availability Improve IT efficiency Elimination of tape positioning, tape errors, and other mechanical issues Improved backup reliability Backup array can be connected to a remote site for data mirrored (disk-to-disk) as a nondisruptive background IT task Raw Performance Results Table 2 shows the CX600 performance percentage gain over the tape drives tested with the large dataset using both FC disks and serial-ata disks as comparison. Table 2. CX600 Performance Gain over Tape Drives Tape Drive Backup Restore SDLT % 30% LTO 30% 35% SDLT % 51% CX400 and CX200 results, with the SDLT 320, LTO, and SDLT 220, are as follows: Backups are up to 13, 19, and 45 percent faster than the tape drives tested. Restores are up to 24, 29, and 46 percent greater. Also note the following: Disk-based backups can also benefit from using CLARiiON SnapView point-in-time snapshot capabilities for faster data recovery and efficient business processing. Tape will be used more for archival and offsite roles, instead of a front-end data collector. When configuring CLARiiON for backups, create an exclusive five-disk RAID 5 configuration with a single LUN per backup server. Multiple systems can share a CLARiiON storage system, with each system having exclusive use of one or more LUNs in the storage array for backup operations. Backup-to-Disk Guide with VERITAS NetBackup 22

23 Appendix A: Tape Drive Characteristics The following factors affect tape drive performance: Media positioning: When a backup or restore is performed, the storage device must position the tape so that the data is over the read/write head. Depending on the location of the data and the overall performance of the media device, this can take a significant amount of time. When you conduct performance analysis with media containing multiple images, it is important to account for the time lag that occurs before the data transfer starts. Tape streaming: If a tape device is being used at its most efficient speed, it is said to be streaming the data onto the tape. Generally speaking, if a tape device is streaming, there will be little physical stopping and starting of the media. Instead, the media will be constantly spinning within the tape drive. If the tape device is not being used at its most efficient speed, it may continually start and stop the media from spinning. This behavior is the opposite of tape streaming and usually results in a poor data throughput rate. Data compression: Most tape devices support some form of data compression within the tape device itself. Highly compressible data will yield a higher data throughput rate than uncompressible data if the tape device supports hardware data compression. This will be true even if the tape device is able to stream the data onto the tape for both the highly compressible data and the uncompressible data. Uncompressible data: If your data is already compressed or is not compressible, then the tape drives will be limited to their native transfer rates. Some file types that are already compressed include video and music files, pictures, zip files, and some database applications, to name just a few. Backup-to-Disk Guide with VERITAS NetBackup 23

24 Appendix B: Related White Papers The following white papers are available on the EMC.com technical library: EMC CLARiiON CX-Series Backup-to-Disk Guide (with CX600, CX400, and CX200) EMC CLARiiON Backup-to-Disk Guide for the FC4700 EMC Designing a Backup Topology for Data on a CLARiiON Storage System : VERITAS NetBackup in SAN Environments : VERITAS Backup Exec in SAN Environments Using the FC4700 and SnapView with Oracle8i EMC CLARiiON Database Storage Solutions: Oracle9i with SnapView in SAN Environments Using CLARiiON MirrorView with Oracle 8i in SAN Environments Storage Technology Choices for Microsoft SQL Server 2000 with CLARiiON Storage Systems EMC CLARiiON Database Storage Solutions: Best Practices for Microsoft SQL Server 2000 in SAN Environments EMC CLARiiON Application Storage Solutions: Disk Backup/Restore of Microsoft Exchange 2000 in SAN Environments EMC CLARiiON Application Storage Solutions: Installing Exchange 2000 with a Microsoft Cluster in SAN Environments EMC CLARiiON Database Storage Solutions: Microsoft SQL 2000 Cluster Installation in SAN Environments : Using EMC SnapView and MirrorView for Remote Backup in SAN Environments EMC CLARiiON Database Storage Solutions: Using EMC SnapView with Microsoft SQL Server in SAN Environments EMC Support Matrix (ESM) Can be found at: Configuring Your FC4x00 Storage System for Use with Backup Software Can be found by EMC customers at: Backup-to-Disk Guide with VERITAS NetBackup 24

25 Appendix C: Related Articles The Enhanced Backup Solutions Initiative (EBSI) Is a vendor-agnostic, industry coalition of storage companies dedicated to helping businesses better protect their mission-critical data with emerging hardware and software technologies for backup that maximize operational efficiency and cost savings. W. Curtis Preston s article, Surprise! Cheap Disks Cure Slow Backup, in Storage Magazine id35_gci828729,00.html Notes several downsides of tape and upsides of disk, and provides an example of how to apply disk. Preston also delivered the keynote speech, titled Rethinking Backup Design at the February 2002 Easing Backup Pain conference sponsored by the Storage Networking Industry Association (SNIA). The article Beyond Backup: Ensuring Data Protection s&subsection=display&article_id= Contains the section Choosing the Right Backup/Recovery Approach, which is a nice quick comparison of disk-to-tape, disk-to-disk, point-in-time, and snapshot. The letter titled ATA Stacks Up from Quantum's co-founder argues convincingly against claims of ATA disk reliability problems. See it at: s&subsection=display&article_id= Scroll down for the second article on the page. Designing to Restore from Disk: Backup Futures 01.htm&page=1 Points out limitations in tape-based backup, and looks ahead to using disk-based point-in-time replication technologies. EMC is working with partners to leverage sophisticated storage array features for backups. A great article discussing this, Special Report: Shortening the Backup Window, appeared in the April 2002 issue of Storage Magazine: ci814808,00.html Backup-to-Disk Guide with VERITAS NetBackup 25