Mount VMFS Datastore manually is sometimes necessary when working with DR plans. A volume that isn’t automatically mounted on the other side has to be mounted manually. Normaly SRM takes care of it.
Also, sometimes when an existing VMFS volume is still present we have an option to keep an existing signature or choose to resignature. What’s the options and the gotchas here? How does this impact the datas which are stored on those volumes?
Keep the existing signature – You basically cannot mount two datastores with the same UUID on the same host. ESXi uses the UUID to reference the device. However, you may un-mount the initial datastore and mount the duplicate datastore with the same UUID. You can also mount a snapshot/replicated lun, while keeping the existing signature, on a host that does not have access to the original lun (DR plans etc…).
Assign a new signature – This will change the UUID and allow it to be mounted. There are some things to bear in mind before you make your choice. Creating a new signature for a drive is irreversible – once a new signature applied, there is no way back. For example if you have datastore with extents, note that such a datastore may only be resignatured once, and all extents must be online. Last note concerning a resignature is that if a datastore is resignatured, the VMs stored on this a datastore must be reassociated with the disk in their respective configuration files and the VM must be re-registered within vCenter.
In this situation it is usually ok to mount the lun without resignaturing because the host to which you mount the lun is likely in a DR site, and as such doesn’t have access to the original lun. Basically, it’s fine not to perform the resignature when mounting the volume on a host that is unable to see the original disk. Resignaturing becomes important when you need to mount a replicated lun on the same host(s) that have the original mounted.
So, how it is done?
You can resignature a disk by using the vSphere Client or using the command line. vSphere client gave me no results recently, but normally it’s very easy. You just do it when you first select your host > configuration > storage > add storage > chose disk/lun > and choose the option you want.
Select Assign new signature or keep existing signature, depending on your needs, and click next, next …
We can list all detected VMFS snapshot volumes with the following command, even if for some reason we aren’t able to mount the volume from within vSphere client (it was my case in a lab recently…).
This command will list the names of the VMFS datastores and their UUIDs.
As you can see in our case we have the output like this:
to resignature the volume. The general syntax is following:
esxcli storage vmfs snapshot resignature –volume-label=<label>|–volume-uuid=<id>
OR use the “M” switch (note it’s a Capital M) to mount the volume as is (keep existing signature):
to mount the volume without resignaturing (use lower case m for temporary mount rather than persistent).
Yes, if you do not wish the volume mount to persist a reboot, the -m switch shall be used instead.
Hope it will help when needed… If you liked this post, just share.