8/10/2019 Vtricks.com-DataCores SANsymphonyV Part 2 Mirrored Virtual Disk

1/5

8/10/2019 Vtricks.com-DataCores SANsymphonyV Part 2 Mirrored Virtual Disk

2/5

It is possible to set up multiple mirror paths between two nodes to enable a failover in case a connection fails butonly two paths will be able to transport mirror traffic simultaneously. Each node will login to its partners targetports so there will always see twice as many paths as physical connections.

If all mirror paths fail for whatever reason and SANsymphony-V still can communicate via its managementnetwork it will stop access on one side to prevent data corruption. More about that will follow in a post aboutpossible failure scenarios.

Disk Pool

As explained each side got its own disk pool and as long as only mirrored virtual disks will be used (and nosnapshots, etc.) the pool utilization will be equal. Snapshots or single vDisks will lead to an uneven utilization.

As long as Auto-Tiering isnt being used. which will be covered in part 5, its recommended to pool physical diskwith identical performance characteristics. When creating a vDisks then the same pool/type of disk should be

http://vtricks.com/?p=243

8/10/2019 Vtricks.com-DataCores SANsymphonyV Part 2 Mirrored Virtual Disk

3/5

used as source on both nodes.

Virtual Disk

The actual mirror and vaiable is achieved on a per vDisk level so every virtual disk should be created as mirroreddisk. the process is the same as for single virtual disks except the fact that a disk pool needs to selected on bothstorage nodes. SANsymphony-V then will create a virtual disk on each node, basically independent copies. OnevDisk will be the preferred/primary one where as the other will be the alternate/secondary one. This is only to tell

the application hosts on which side/node where to access storage primarily. As soon the wizards completes SSVwill create the vDisks, automatically add the mirror paths and after a short recovery to sync the bitmap which iskept in RAM and the SAUs the vDisk is ready to go.

Note: SANsymphony-V will only create up to 2 mirror paths automatically as depicted in the screenshot above. If

8/10/2019 Vtricks.com-DataCores SANsymphonyV Part 2 Mirrored Virtual Disk

4/5

more are required those need to be added manually.

And this is how it will look like once the vDisk has been created.

To wrap up this post allow me to quote some state out of the SSV Webhelp documentation to provide an overviewof possible virtual disk states:

Up-to-date Data on both servers is identical (synchronized) and the virtual disk is capable of I/O operations.

Log recovery needed The data on one server is not up-to-date and has to be recovered from the other server using a log recovery. This is a temporary status until a mirror path is available so that synchronization can takeplace.

Full recovery needed The data on one server is not up-to-date and has to be recovered from the other server using a full recovery. This is a temporary status until a mirror path is available so that synchronization can takeplace.

Log recovery pending The data on one server is not up-to-date and has to be recovered from the other server using a log recovery. The mirror path has been found and the recovery will begin momentarily.

Dual log recovery pending - The data on one server is not up-to-date and a log recovery is in process. I/Ooperations from the host are being logged on the other server, which must also be recovered after the first logrecovery is complete. The mirror path has been found and the recovery will begin momentarily.

Dual full recovery pending - The data on one server is not up-to-date and a full recovery is in process. DuringI/O operations on the other server, an event occurred which caused the second server to require a full recoverythat will begin after the first recovery completes. The mirror path has been found and the recovery will beginmomentarily.

Full recovery pending The data on one server is not up-to-date and has to be recovered from the other server using a full recovery. The mirror path has been found and the recovery will begin momentarily.

In log recovery The data on one server is currently in log recovery. This is a temporary state. Please wait for recovery to complete.*

In full recovery The data on one server is currently in full recovery. This is a temporary state. Please wait for recovery to complete.*

Status not defined Information is unknown because the server is down, or unreachable and the server cannotcommunicate. Ensure servers are started and verify network connectivity.

Action may have to be taken, see Forcing On-line in this topic for important information.

Unknown The DataCore Server is up, but does not know what the status is because the status from the other DataCore Server is not defined. Action may have to be taken, see Forcing On-line in this topic for importantinformation.

Double failure Both servers have failed and the source of the failure should be determined and corrected. Thedata on both servers should be evaluated and the most valid side should be forced up in order to recover. Action

8/10/2019 Vtricks.com-DataCores SANsymphonyV Part 2 Mirrored Virtual Disk

5/5

will have to be taken, see Forcing On-line in this topic for important information.

Source: http://www.datacore.com/SSV-Webhelp/mirroring_and_mirror_recovery.htm