Host Offload Throttling Must be Enabled Before Upgrading to V8.1.0.0

Content

Problem summary

Spectrum Virtualize software supports SCSI offload commands (such as WRITE SAME and XCOPY). Hosts use these, for example, to format new filesystems, or copy volumes without the host needing to read and then write data.

V8.1.0.0 advertises support for SCSI UNMAP to hosts. Some host types will respond to this by issuing WRITE SAME UNMAP commands, requesting large amounts of I/O. If the underlying storage cannot handle the amount of I/O that is generated, then performance of volumes may be impacted, and in extreme cases, node warmstarts may be caused by internal I/O timeouts.

Spectrum Virtualize offload throttling limits the concurrent I/O that can be generated by WRITE SAME and XCOPY commands - which can prevent MDisk overloading. Note this will limit the rate at which host features such as VMWare VMotion are able to copy data.

Procedure to allow upgrade to V8.1.0.0

Customers who require to upgrade systems to V8.1.0 before a fix is available must manually enable the offload throttling feature as follows.

1. Run the svcupgradetest utility to obtain the recommended bandwidth throttle value
   - for systems managing any enterprise or nearline storage, the recommended value is 100 MB/sec.
   - for systems managing ONLY tier1 flash or tier0 flash, the recommended value is 1000 MB/sec
2. Enable the offload throttle, using the CLI command:
   mkthrottle -type offload -bandwidth bandwidth_limit_in_MB
3. Re-run svcupgradetest and confirm that the offload throttle error is no longer present.
4. Start the upgrade to V8.1.0.0 using the svctask applysoftware CLI command.

Fix

The V8.1.0.1 PTF includes measures to prevent overloading of MDisks. This will not affect XCOPY commands, and so will not limit the speed of VMWare VMotion XCOPY operations.