A Detailed Review Abstract The white paper describes how the EMC Disk Library can enhance an IBM Tivoli Storage Manager (TSM) environment. It describes TSM features, the demands these features place on back-end disk and tape backup subsystems, and how the Disk Library meets those demands. February 2010
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Table of Contents Executive summary...4 Introduction...4 Audience... 4 TSM disk and tape resource design...4 Storage pools... 4 Copy storage pools... 4 Media independence... 5 Progressive incremental... 5 Backup and reclamation policies... 5 The value of the Disk Library to TSM environments...6 Daily schedule... 6 Backup and restore performance... 6 Migration... 7 Reclamation... 7 Copy storage pools... 7 Reliability... 7 Scalability... 8 Migrating to the Disk Library... 8 Conclusion...8 References...8 A Detailed Review 3
Executive summary EMC Disk Library can help any IBM Tivoli Storage Manager (TSM) customer in a number of ways, including: Reducing the valuable time and resources spent migrating from disk to tape Helping to complete the daily schedule of backups, migrations, and other operations Freeing up tape drives for a restore Reducing or eliminating tape handling and the inherent risks of sending tape cartridges offsite Introduction The purpose of this white paper is to describe how the EMC Disk Library enhances an IBM TSM environment. It describes some of the key features of TSM, and the demands those features place on backend disk and tape backup subsystems. In doing so, this paper explains how the EMC Disk Library can satisfy those demands, adding value to a comprehensive backup environment. Audience This paper is intended for technical field consultants, customer engineers, and customers experienced with TSM and Disk Library operations. TSM disk and tape resource design To understand the value of the Disk Library in a TSM environment, it is helpful to familiarize yourself with how TSM uses its disk and tape resources to manage backup and archive data. Storage pools TSM stores data in storage pools. A storage pool is a group of storage media of the same type on which backup and archive data can be stored. There are two types of storage pools: primary and copy. Primary storage pools receive backup and archive data written by the TSM server or client. Copy storage pools are created by copying data from a primary storage pool; they are used to create an extra copy of data. The typical application for this extra copy is offsite storage of data. Both primary storage pools and copy storage pools can be disk, tape, or optical media. Most TSM customers back up client data to a TSM disk storage pool first because TSM client data cannot be written directly from multiple clients to the same tape drive. The interleaving of data from multiple clients backing up simultaneously to the same tape drive (common in backup applications like Veritas NetBackup, EMC NetWorker, and others) does not exist in TSM. In other words, if a TSM client is backing up directly to tape, it has exclusive access to that tape drive for the duration of its backup. This is true whether the backup is LAN- or SAN-based. TSM permits multiple clients to simultaneously write to a disk storage pool, thus allowing far more clients to back up at once. In most cases, data in the disk storage pool is migrated using an automatic process to a primary tape storage pool. This migration process consumes a certain amount of the daily schedule and tape-drive resources. Copy storage pools Most customers make a redundant copy of their primary storage pool so the data can be sent offsite. TSM calls this redundant copy a copy storage pool. It is typically updated every day with all new backup data using the backup stgpool command. To update the copy storage pool, TSM looks in its internal database and compares the list of files in the primary and copy storage pools. TSM only copies the backup data from A Detailed Review 4
the primary storage pool that is not already in the copy storage pool. That is, TSM only copies the changes in the primary storage pool since the last time backup stgpool was run. If the source media for the copy storage pool is tape, the process used to create the copy storage pool tapes requires two tape drives per thread, as well as a significant amount of time in the daily schedule. Media independence Unlike other backup products (such as Veritas NetBackup), TSM has no restrictions on media types or size. The primary and copy storage pools can be any media type or size. For example, the primary could be disk, and the copy could be DLT tape. Or, the primary could be 9840 tape, and the copy could be LTO tape. Because backup and copy processes track the data by file and not just at the tape level, TSM is referred to as file-centric, as opposed to tape-centric. This file-centric view of data allows TSM to easily move data from one media type to another as circumstances demand. One of the problems backup administrators face is how to migrate from an old technology media to a new one, for example migrating from DLT7000 to LTO. In other backup products, it is necessary to keep old tape technology in place until all the backup media of that type has expired. This can require older tape drives to be retained for years past their usefulness, just in case a restore is required from the old tape media. With TSM, it is a straightforward process to install new tape technology and move the data from old tape media to the new, using the move data command. A user can even migrate from one TSM server to another. Depending on the number of tapes involved, this process can take considerable time; however, it can be started and stopped at will. Progressive incremental Traditional backup products use a scheme of full and incremental backups. A full backup is one that backs up all the files on a given client or file system. An incremental backup is one that backs up only those files that have changed since the last full or incremental backup. Traditional backup products usually employ a full backup once a week, with incremental backups on the remaining days of the week. TSM backups are usually incremental forever what TSM refers to as progressive incremental. The first time a given client or file system is backed up, all the data is backed up, resulting in a traditional full backup. Each subsequent backup is incremental. TSM does not need to take a full backup of files that have not changed. One reason most traditional backup products use regular full backups is because of the unreliable nature of tape media. The concern is that unless multiple full backups occur at regular intervals, the loss of a single backup tape would create an unrecoverable situation. TSM handles this concern using copy storage pools, which create an extra copy of the data (as described in Copy storage pools on page 7). This ensures that the loss of a tape cartridge will not mean the loss of the only backup copy. The second reason for the traditional backup and incremental scheme is to prevent the data needed to restore a whole client or file system from spanning too many tape cartridges, which would slow down restore performance. TSM handles this concern with a feature called collocation, which attempts to keep a given client s data on the minimum number of tapes. Backup and reclamation policies Backups in TSM are policy-based. Customers can establish policies that govern: Which files on a server will be backed up or archived To which media the files will be backed up or archived How many versions of various files will be retained How long the versions will be retained A Detailed Review 5
These policies can be very simple, or they can be as complex and granular as the customer wants to make them. Because of the policy-based nature of TSM, the data on a tape cartridge does not expire all at once. As data on a tape cartridge expires, the cartridge becomes more and more logically empty. Eventually the amount of remaining data drops below a predefined threshold and needs to be reclaimed. This reclamation process mounts the tape to be reclaimed, and mounts another tape with free space, and copies all the remaining valid data from one tape to another. The tape cartridge that was the source for the reclamation is now empty, and can be reused as a scratch tape. Reclamation requires two tape drives. Because the valid data can be scattered over the whole tape cartridge, performance during reclamation tends to be quite poor because most tape technologies perform poorly when frequently stopping and starting. The value of the Disk Library to TSM environments Because of the performance and flexibility of the Disk Library, it can often replace both the primary disk and tape storage pools. Moreover, if an extended SAN is employed, the Disk Library can be used at a remote location to provide the additional redundancy of a copy storage pool. The following sections describe the benefits of using the Disk Library in a TSM environment. Daily schedule During a typical 24-hour TSM schedule, the TSM server must do the following: Perform backups and archives Perform migrations from disk to tape storage pools Update copy storage pools from primary storage pools Back up the TSM database to tape Check out offsite tapes and check in tapes returning from offsite Expire inventory (clean up expired records from the TSM database) Reclaim tape cartridges and return them to scratch status Each of these tasks (except for expiration) requires resources from the tape library and drives. TSM administrators with a large number of hosts, or a small tape library, must make difficult scheduling decisions to avoid overlapping these activities. Sometimes they are forced to back up hosts less often or back up only portions of the host data just to create additional time in the schedule. If one or more tape drives experience a hardware problem, the schedule can fall even further behind. This is a definite pain point for customers. When talking to a TSM customer, it is always to good idea to walk through a typical 24-hour schedule to determine how much time is spent performing each of these tasks. It is not unusual for a TSM administrator to frequently modify schedules to keep these competing activities from overlapping. If the TSM server s activities come close to filling the 24-hour schedule, the customer is a prime candidate for a Disk Library. The following sections explain why. Backup and restore performance Many customers use disk storage pools whose performance is much slower than the total bandwidth of the Disk Library. Many tape technologies are much slower when compared to virtual tape drive speeds especially where physical tape cannot be streamed effectively. In these cases, there can be a significant performance benefit using the Disk Library for backups. With TSM s progressive incremental scheme, disk-to-tape migration and reclamation spread backup client data over many tape cartridges. This can make a restore of a given backup client s data very timeconsuming. This can be minimized using collocation, but only to a certain extent. Using the Disk Library for restores is faster than traditional tape because much of the time spent restoring from tape is taken by mounting and positioning the tape to locate the restore data. The Disk Library removes all the delays that would occur because of tape movement. The actual transfer of the data from the Disk Library to the restore A Detailed Review 6
host is the only time-consuming task. Even in this regard, because of its high single-stream throughput, the Disk Library is an improvement over traditional tape. Migration Many TSM customers install far less disk than their primary storage pool requires and have only enough disk capacity to accommodate a few days of new backup data. To create room for new incoming data, they must migrate backup data frequently from the disk pool to tape (this can occur daily in some cases). Because the Disk Library permits the customer to create many more virtual tape drives than would typically be purchased in a real tape environment, a customer can direct far more backups directly to the Disk Library, reducing or eliminating the need to stage the client data to disk first, and migrate it to tape later. When the Disk Library replaces both the primary disk and tape storage pool, the entire daily migration process is eliminated; this frees time in the schedule, and reduces tape-drive resources. Reclamation TSM will need to reclaim tape cartridges, whether they are real tape cartridges or virtual tape cartridges in a Disk Library. However, the performance of reclamation in a Disk Library will be significantly faster than that which can be achieved with a conventional tape drive. The first reason is that the transfer speed of a virtual tape drive is several times faster than most physical tape drive technologies. The second reason is that, during reclamation of a real tape cartridge, a lot of time is expended stopping and starting the tape drive searching for the valid data among the empty spaces on the tape cartridge. These scans through the tape happen almost instantaneously with a virtual tape drive. Copy storage pools When a TSM server updates a copy storage pool, it requires an input and output tape drive for each copy stream. If a Disk Library s virtual tape drives are used as the input, more real tape drives are available for the output tape streams. Twice as many copy streams can be performed at once, cutting the time to complete the process in half. If a customer installs a Disk Library at a remote location and accesses it using an extended SAN, it is no longer necessary to remove physical tape cartridges from a tape library and send them offsite. This can dramatically improve (reduce) the time it takes to move data from one location to another. This also eliminates operator handling and shipping charges for the tapes, and removes the risk of data loss due to contamination or damage to the tape media. In the event of a data loss, the restores from a Disk Library at the remote site will be significantly faster than restoring from physical tape drives. Furthermore, in many remote site locations, cost constraints mean there are far fewer tape drives than exist in the production environment. With a Disk Library, customers can create as many virtual tape drives in their remote site as the production Disk Library, eliminating a potential bottleneck during recovery. Reliability The Disk Library uses an EMC storage system with its inherent high-availability features. This provides for a more reliable platform for the backup. Because of the many moving parts of a physical tape drive, it is demonstrably less reliable than the welldesigned, protected disk storage found in the Disk Library. The physical tape cartridges themselves are a single point of failure. Cartridges age and become less reliable after multiple uses and many customers do not have a formal process in place to replace cartridges over time. Cartridges are also subject to risk of damage or loss when they are removed from the tape library and shipped offsite. A Detailed Review 7
Scalability Many customers are only able to buy just enough tape-drive bandwidth to meet their minimal requirements. When a customer runs out of tape-drive capacity, they are forced to purchase and install additional tape drives, and often upgrade or replace their tape library. With the Disk Library, it is a simple matter to create and define additional virtual tape drives. However, in this case, TSM licensing implications should be considered to ensure no additional cost burden is incurred. Migrating to the Disk Library Because of the media-independent nature of TSM, customers implementing a Disk Library will be able to emulate the same type of media they are currently using or choose a different one. If they would like to eliminate the old tape media they are currently using, it is a straightforward process to move the active TSM data from the old media to the Disk Library even if they want to change to different tape-drive emulation. They can also migrate large volumes of data from their current tape infrastructure to the Disk Library to free up tape resources for use as copy storage pools. Conclusion The Disk Library will be an attractive offering for any TSM customer who: Uses valuable time and resources migrating from disk to tape Is considering upgrading their tape library or adding drives because they are out of resources Has trouble completing the daily schedule of backups, migrations, copy storage pools, and so on Is forced to cancel backup processes in order to free up tape drives for a restore Backs up less often than desired, or performs incomplete backups, because they don t have enough tape resources to get the job done Is unable to complete nightly backups any time a single tape drive is offline for repair Wants to migrate away from outdated or unreliable tape technologies and reduce maintenance costs Wants to reduce or eliminate tape handling and the inherent risks of sending tape cartridges offsite Is not meeting their restore time objectives References The following white paper can be found on Powerlink and EMC.com: EMC Disk Library DL4106, DL4206, and DL4406 Version 3.2 - Best Practices Planning A Detailed Review 8