vSphere Storage Appliance

Currently, my iSCSI SAN device offers snapshotting capability. I've implemented this for several volumes holding VMFS datastores that hold user files (home directories, profiles, etc). I'd like to be able to access those snapshots without altering the data in the snapshots in order to provide an easy way to restore accidentally altered/deleted files within the time frame the snapshots cover.

I'm using an EqualLogic PS5000 and enabling access to the snapshots to a test ESXi machine to see if I can do this. I've been able to get the ESXi server talking with the EqualLogic array and several volumes. If I present the snapshot as read-only it does not mount it at all but does recognize it as an iSCSI target. It does put a few errors into the log and the events list. I'll post the errors shortly.

I've searched around the documentation and all I can find is:

vsp_40_esx_server_config.pdf, p106: "When you mount the VMFS datastore, ESX allows both reads and writes to the datastore residing on the LUN copy. The LUN copy must be writable. The datastore mounts are persistent and valid across system reboots.

Because ESX does not allow you to resignature the mounted datastore, unmount the datastore before resignaturing."

This makes me think that it's literally impossible.

If that is the case, is it possible to have ESX/ESXi present a VM with a read-only disk? I know that I can use Linux and just use `mount -o ro` but I'm considering this for others in my office who really wouldn't know what to do. The closest I see for this is to use the VMDK as independent, non-persistent.

No it is not possible - in intercting with the VMFS volume your ESX host will need to be able to read and write to the volume -

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As you've noted to be able to resignature a LUN ESXi must to able to write to it. Otherwise you can't use a snapshot LUN with ESX(i). If you do go with non-persistant mode, the guest OS will still be able to write to the virtual disk, but if you power off the VM or revert to a snapshot all the disk changes will be discarded.




Dave

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I'm not looking to resignature the VMFS volume but rather just mount the EQL target snapshot. The ESXi test machine does not have access to the original volume and is unmanaged so resignaturing should be unnecessary as both the name and the UUID will not collide with existing volumes.

My primary goal is leave as much as possible untouched. If I can't present a read-only target to ESX/ESXi and use it as a volume, the next best thing is to use the volume such that the disk is not touched. If I'm reading correct, using the VMDK as non-persistent should have a similar effect to opening the VMDK with a VM snapshot. By this, I mean that the changes are written out to a separate VMDK file such that when I power off the VM, the original VMDK has never been touched. This solution would be acceptable assuming that I have my information correct.

That is correct. Using the VMDK as non-persistent should have a similar effect to opening the VMDK with a VM snapshot in read only mode. Yes, the changes are written out to a separate file and when the VM is powered off, the original VMDK has never been touched and remains the same.