Storage XenMotion Tampa Technology Project

Storage XenMotion Tampa Technology Project Andrei Lifchits XenServer Storage

Overview Feature overview Use cases Bird s-eye view of operation Feature limitations and potential pitfalls API/CLI/GUI walkthrough Under the hood 2

Recall: Existing Feature XenMotion (live VM migration) Host A Pool Host B VM SR VDI 3

Recall: Existing Feature Requires shared storage Host A Pool Host B VM SR 1 VDI SR 2 4

Feature Overview Two new operations: ᵒ Cross-pool VM migration Moves storage VM migrate part the same as in XenMotion ᵒ Live VDI migrate Actually the same thing Supported Storage Repository types: ᵒ iscsi ᵒ HBA ᵒ NFS ᵒ local LVM or EXT 5

Use cases 1. Upgrade a storage array 2. Provide tiered storage arrays 3. Upgrade a pool with VMs on local storage 4. Rebalance VMs between XenServer pools, or CloudStack clusters The Cloud was the major use case we had in mind when designing this 6

Storage XenMotion Use Case: Upgrade a Storage Array, or Provide Tiered Storage Host A Pool Host B VM SR 1 VDI SR 2 7

Storage XenMotion Use Case: Upgrade Pool with VM on Local Storage Host A Pool Host B VM SR 1 VDI SR 2 8

Storage XenMotion Use Case: Remove Host with Local Storage from Pool Host A Pool Host B VM SR 1 VDI SR 2 9

Storage XenMotion Use Case: Rebalance VMs between standalone XenServers Host A Host B VM SR 1 VDI SR 2 10

Storage XenMotion Use Case: Rebalance VMs between XenServer Pools Host A Pool Host B Host A Pool VM SR VDI Host B SR 11

Feature Overview: Guiding principles Doesn t interfere with VM power state operations ᵒ Different roles: VM admin vs. cloud admin Extra network IO won t interfere with Xapi s management interface ᵒ Can choose any network for data (disks + memory) transfer This feature requires reliable infrastructure ᵒ Errors are not retried 12

Operation: Bird s-eye view Cross pool migration and VDI migration consist of the following: 1. Synchronously mirror VDIs between source and destination ᵒ Snapshot first to track new writes 2. Create new VM object on destination pool 3. When copy complete, migrate VM as usual 13

Operation: Difference between XenMotion What gets sent across the wire? XenMotion Storage XenMotion VM memory VM memory VM disks New writes to VM disks (VM metadata kept on Master) continuously Associated VM objects snapshots, RRDs, alerts 14

Feature Overview: Supported Configuration Any running VM with any OS with PV drivers CPU hardware on destination: must have compatible flags No VMs with VDIs in Integrated StorageLink SRs No more than 6 VDIs, and no more than 1 VM snapshot No more than 3 concurrent migrations per host No VMs with PCI pass-through enabled Same as XenMotion Restrictions: ᵒ HA and WLB must be disabled on source and destination pool (temporarily) ᵒ No DVSC integration 15

Feature Overview: CPU compatibility CPU on destination checked before migrating VM Can migrate to a newer compatible CPU ᵒ One-way upgrade Cannot migrate to an older or incompatible CPU ᵒ Migration will not be allowed No CPU masking, like in pools 16

Feature Overview: Caveats Minimum network or storage throughput requirements currently unknown Can t check whether destination SR has space available for incoming VDIs if you fill up an SR, your migration will fail to complete Extra storage is required on the source SR, so you must be careful when migrating VMs off of a full SR IO performance inside guest will be reduced during mirror because of synchronous writes 17

Feature Overview: CLI walkthrough xe vm-migrate ᵒ New params: remote-address, remote-username, remote-password, remote-network, vif, vdi Extends the original vm-migrate command Bold params are required to enable cross-pool migration vif and vdi map VIFs to target networks and VDIs to target SRs remote-network specifies the network used for data transfer Can use host/host-uuid to specify host on pool to send VM xe vdi-pool-migrate ᵒ Params: uuid, sr-uuid uuid of target VDI sr-uuid of destination SR 18

Feature Overview: CLI example xe vm-migrate vm=demo remote-address=10.80.228.29 \ remote-username=root remote-password=passw0rd \ destination-sr-uuid=fac83e53-7379-d2e7-5bb7-1a2ba8345a3b OR: xe vm-migrate vm=demo remote-address=10.80.228.29 \ remote-username=root remote-password=passw0rd \ vdi:9631baba-9223-4332-8c85-bfe21714f11f=fac83e53-7379-d2e7-5bb7-1a2ba8345a3b 19

Feature Overview: CLI example xe vm-migrate vm=demo remote-address=10.80.228.29 \ remote-username=root remote-password=passw0rd \ destination-sr-uuid=fac83e53-7379-d2e7-5bb7-1a2ba8345a3b Host A VM demo Host B 10.80.228.29 SR VDI 9631 SR fac83e53 20

Feature Overview: API walkthrough Host.migrate_receive host:ref network:ref options:map Result = receive_token VM.migrate_send vm:ref receive_token live:bool vdi_sr:map vif_network:map options:map Result = None VM.assert_can_migrate vm:ref receive_token live:bool vdi_sr:map vif_network:map options:map Result = None VDI.pool_migrate vdi:ref sr:ref options:map Result = vdi:ref 21

Feature Overview: GUI walkthrough 22

Feature Overview: GUI walkthrough 23

Under the hood: changes in XenServer Some re-architecting of Xapi ᵒ In preparation for the driver domains 1 New xapi-storage interface NBD (network block device) protocol used for synchronous mirroring 1 http://blogs.citrix.com/2012/05/17/introducing-windsor-a-new-xen-based-virtualization-architecture 24

Under the hood: VDI operations For each VDI: ᵒ Snapshot VDI and synchronously mirror all subsequent writes to destination SR ᵒ Copy the snapshot to destination SR ᵒ Finally, compose those writes onto the snapshot on the destination SR Continue to mirror all new writes Each of these operations occurs sequentially for each VDI ᵒ but each VDI mirror continues until the VM migration is complete VM memory is copied only after final VDI compose is complete VDI 1: snapshot & start mirroring VDI 1: copy snapshots VDI 2: snapshot & start mirroring VDI 2: copy snapshots Copy VM memory 25

Architecture: VDI copying In the background, while mirroring Optimization: start with most similar VDI ᵒ Another VDI with the least number of different blocks ᵒ Only transfer blocks that are different ᵒ Content ID for each VDI ᵒ Worst case is a full copy ᵒ Stepping stone to a better VMPR feature 26

Troubleshooting Problems Check the Logs tab in XenCenter for the VM and/or hosts involved Main log file on control domain: /var/log/xensource.log ᵒ Very verbose, but might shed light on nature of error /var/log/messages generally useful 27

Summary Shared storage no longer required to migrate VMs Two new operations: migrate VM & migrate VDI Cross-pool migration comprised of VDI snapshotting, copying, and mirroring Both operations require space on source and destination SR 28

VHD basics Many SRs implement VDIs as VHD trees VHDs are a copy-on-write format for storing virtual disks VDIs are the leaves of VHD trees Interesting VDI operation: snapshot (implemented as VHD cloning ) A RW RO A: Original VDI B: Snapshot VDI RW B A RW 30

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