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peetz
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How to prepare for a planned SAN downtime

Hello all,

our ESX 3.0.2 hosts use SAN volumes that are on three different storage boxes, two HP XP12000 and a EMC Clariion CX700.

We will soon have a planned downtime of the Clariion, i.e. the Clariion LUNs will then be completely unavailable for a few hours.

We noticed at earlier occasions that the unavailabilty of a SAN LUN results in an overall system slowness, interruptions in storage access and very poor VM performance, even with all other SAN LUNs (and VM stored there) that are still available.

That means: The Clariion downtime will most probably severly affect the overall performance of the ESX hosts and the performance of the VMs that are stored on the XP12000 LUNs (although they will be still available).

This is true even if we power off all VMs that are stored on the Clariion LUNs before the downtime.

I guess this is caused by the ESX hosts periodically trying to access the LUNs that are down which somehow also blocks access to the LUNs that are still available.

How can we avoid this situation? Is there any way to gracefully tell an ESX host that a SCSI target is or will be unavailable and that it should not try to access it? Is there any way to just dismount the VMFS file systems that are located on these LUNs?

I tried to use the Disk.MaskLUNs option to hide the LUNs that will go down, but I had limited success: even after multiple HBA-rescans part of the hidden LUNs were still accessed on one SAN path. The option will most probably only work after a host reboot (which we want to avoid).

So to say it short: Is there any safe way to prepare a host for a planned SAN storage downtime?

Thanks and best regards

Andreas

Twitter: @VFrontDe, @ESXiPatches | https://esxi-patches.v-front.de | https://vibsdepot.v-front.de
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