Snapshot of an RDM disk with ESX 3.x (crash consistency)

[yaklein]

Hi floks,

I m having a VMs with RDM devices as disks and I wish to make snapshots of those disks. I have external snapshots capabilities (recall that the ESX currently do not support RDM snapshots) using my SAN provider, however I m worried about the crash consistency (e.g., one of the VM is our Exchange server).

Is there any functionality regarding halting the service in the VM prior to the snapshot action? can I use MS VSS in the VM (i.e., does ESX 3.5 support VSS)? Does the ESX "VM Suspend" functionality ensure crash consistency?

Thanks,

[Gabrie1]

I think if you want to use VSS you will have to write a script for it. Making snapshots of Exchange is kind a tricky like you guessed already You might be able to wirte a script that uses VSS and tells Exchange to clean its cache and then trigger the SAN to do a snapshot. Looks like ESX doesn't have to do anything with it. Would be different if you were running on VMDK. What were your reasons to switch to RDM instead of VMDK? Just cursious, because I here a lot about VMDK performance being equally to RDM now in ESX 3.x.

Gabrie

[yaklein]

Hi Gabrie,

I also think that there is no performance difference between RDM and VMDK. I jsut use RDM as a second disk for compatability reasons. I can use my SAN (EqualLogic PS) for the snapshots, I just wonder what is the best way for the quiece. I used VSS with the reguilar server (before I moved it to VM). However, what is the recommended way now: does VMware has a "VMware VSS" way to stop service and flush cache? Does the VM support VSS transparently? Does VM-Suspend do a cache flush?

Is there any VMware publication, white paper, scenario case?

Thanks,

Yaron

[Gabrie1]

There is no VMware <-> VSS integration at this time as far as I know. VMware does however have an option to send a quiece to the OS, but this is not Exchange aware and as far as I know, this is not the right method to use for exchange backup. I'd just use your normal backup solution like you did before and have that software do the talking to VSS.

Gabrie

[yaklein]

Thanks Gabrie,

Yaron