Q

What to do when VMware Storage vMotion falters

When a VM is being moved with VMware Storage vMotion and the migration doesn't execute properly, there are several ways to pinpoint the problem.

What should I check if a VMware Storage vMotion operation fails?

VMware Storage vMotion is a sophisticated tool with complex software and numerous hardware dependencies. Since numerous potential errors can arise during a Storage vMotion process, there is no single universal cause or troubleshooting path to recommend. However, there are some common tips that might help during the diagnosis.

For example, any error message that suggests insufficient disk space on the data store typically means just that -- the destination volume does not have enough physical storage space to receive the migrated VM. It might be possible to free space by moving existing VMs to another volume or selecting a different destination for the Storage vMotion process. Other tactics include freeing space by deleting old snapshots and removing outdated VMFS volumes. If space is still needed, you may need to add disks to increase storage capacity.

When Storage vMotion fails to copy disks outright, it usually means that the migration was disrupted because the source could not reach the destination data store. This is often caused by SAN or LAN issues. For example, a highly congested LAN segment might have too much latency between the source and destination storage locations. Perhaps there is a problem with a switch or other network device. In extreme cases, there may be a problem with the destination storage subsystem. This type of problem will require careful and systematic troubleshooting to determine and correct the root cause.

If the VMware Storage vMotion process fails repeatedly at a fixed point or percentage of completion, there may be a problem with the destination storage array -- or another device in the storage network path -- and the way that device interprets vStorage API for Array Integration (VAAI) commands. In many cases, the underlying trouble might be traced to an older or unsupported storage array that cannot handle VAAI, or it could be that the storage array needs a firmware update to achieve compatibility. If the compatibility problem cannot be resolved, it may be necessary to disable VAAI support during Storage vMotion cycles.

 

This was first published in May 2014

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