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etotman
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Contributor

SAN snapshot won't boot

I'm trying to boot a SUSE 10 VM from a SAN snapshot. I'm running ESX 3.0.1 attached to a Compellent SAN. The VM is configured to boot from the SAN using RDM. This is the error:

Waiting for device /dev/disk/by-id/scsi-123456789000012-part5 to appear:.........not found -- exiting to /bin/sh

I abbreviated the scsi ID for clarity. The problem is the last part of the scsi ID changes (the volume serial number) when I map the snapshot. On the ESX server I tried setting LVM.EnableResignature to "1" but this didn't make a difference. Any ideas?

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bobross
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Are you using ESX or SAN snapshot? You can't boot or otherwise use RDM from an ESX snapshot. If you use SAN snapshot on Compellent, you must change LVM.EnableResignature as you did but also rescan the HBAs for the new LUN in order for the snap LUN to appear. But I don't recommend (at all) using SAN snaps on Compellent for booting a VM - they are not application consistent whatsoever and in fact may be totally unusable. Not quite user-friendly. You'll end up wasting a lot of time dealing with trying to get the VM and its apps up and running. There is a workaround - quiecse the VM before snapping, but again that's not user-friendly at all, since the entire point of VMs on SAN is to keep them running. In fact Compellent does not recommend booting VMs from SAN at all - they have "no specific recommendation" per their best practice document.

etotman
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Contributor

Thanks for the reply. I'm using SAN snapshots and I powered down the VM before creating each snapshot. If the VM is off or otherwise quiecsed, I don't understand why there would be a problem. Anyway, the fix was to change the scsi id in /boot/grub/menu.lst and /etc/fstab to match the new volume id.

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bobross
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OK. You needed to do that for sure; I had assumed you did already. Anyway, it must be nice to work in a shop where you can power off the VMs; we can't. So we use CDP which gives us the ability to create VM snaps at any point in time without quiescing.

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