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josthimerMD
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MSCS Stun

Post by josthimerMD » Apr 10, 2013 1:49 pm

We know it isn't supported but has any one had success using Veeam to backup MSCS VMs that use the Microsoft iSCSI initiator for cluster disks?

Often times the backup occurs without incident but occasionally the stun from the snapshot removal is long enough to cause the cluster to fail and move the clustered disk to another node.

We've considering increasing disk performance and tweaking heartbeat values for MSCS but are interested in what other have done.

foggy
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Re: MSCS Stun

Post by foggy » Apr 10, 2013 4:23 pm

Jeff, I'm a bit confused regarding what are you actually backing up? Disks connected via in-guest iSCSI initiator are skipped during VM processing and, as far as I know, MSCS requires SCSI bus sharing for storage, which disables the ability to make snapshots at all.

tsightler
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Re: MSCS Stun

Post by tsightler » Apr 10, 2013 4:32 pm 1 person likes this post

@foggy It's somewhat common, though unsupported, to use in-guest iSCSI initiator to create the shared SCSI bus rather than using VMware SCSI bus sharing, which has many limitations. I've seen both Oracle RAC and MSCS clusters configured this way. You're right of course that this means the shared disks themselves cannot be backed up by Veeam, but the rest of the OS disks can be backed up normally using this setup since VMware will still allow the snapshot, although the snapshot removal can cause exactly the issue the user is posting about (which is at least one of the reasons this method is not supported). Overall though it works pretty well, but in general it's suggested to increase the timeouts for failover if you're using snapshot backups of the OS/App disks.

foggy
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Re: MSCS Stun

Post by foggy » Apr 10, 2013 4:42 pm

Always learn something from your posts, Tom. ;).

tsightler
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Re: MSCS Stun

Post by tsightler » Apr 10, 2013 5:08 pm

BTW, I should probably clarify my statement, use of in-guest iSCSI for MSCS is supported by VMware (I'm less sure about Microsoft) according to VMware KB 1037959. While it's a very long and complex KB article, it specifically states the following:
In-guest iSCSI software initiators: VMware fully supports a configuration of MSCS using in-guest iSCSI initiators, provided that all other configuration meets the documented, supported MSCS configuration. Using this configuration in VMware virtual machines is relatively similar to using it in physical environments.
However, it's the use of snapshots and other technologies such as SVmotion on such VMs that is not supported, since they can cause short periods of non-availability that can lead to failover or other problems.

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