Jan 042018
 

(Disclaimer: I am by no means an expert with XenServer. So please don’t take anything you read here for granted. It’s my own experience and what I found in documentation and online.)

In my previous post, I described how to add a Storage Repository to a XenServer using the xe command line tool.

Now, since I have installed the device driver for the RAID controller, created a RAID 5 and added it as Storage Repository (in the same way as described in the linked article), I want to get rid of the SATA drive which I had added as a temporary measure. Guess what, there seem to be no way of doing that using the XenCenter tool (even though the second link below mentions a “Detach” option I could not find it, see the disclaimer above). So, again, it’s the xe command line to the rescue.

xe help

writes a list of supported commands to the console which only contains one command with an sr- prefix: sr-list. Only if you tell it to give you a complete list, you will see what we need here, the sr-destroy command.

xe help --all
[... very long list of commands ...]
xe help sr-destroy
command name            : sr-destroy
        reqd params     : uuid
        optional params :
        description     : Destroy the SR.

But where do we get that uuid? Simple, by asking for it:

xe sr-list
[...]
uuid ( RO)                : 3f1d80c6-929a-f547-9ab1-63a2ca638cbf
          name-label ( RW): XenServer Tools
    name-description ( RW): XenServer Tools ISOs
                host ( RO): xenserver1
                type ( RO): iso
        content-type ( RO): iso
[...]
uuid ( RO)                : <UUID of SR>
          name-label ( RW): temporary-sata-disk
    name-description ( RW):
                host ( RO): xenserver1
                type ( RO): lvm
        content-type ( RO): user

As you can see, there is one Storage Repository with the label temporary-sata-disk. That’s the one I want to remove (the actual list is longer). So

xe sr-destroy uuid=<UUID of SR>

should delete that Storage Repository, right?

No, of course not, you get the error message

The SR is still connected to a host via a PBD. It cannot be destroyed or forgotten.
sr: <UUID of SR> (temporary-sata-disk)

There is also an sr-forget command but it displays the same error message.

So simple guessing doesn’t get us any further. Maybe we should read the docs? Nah, we don’t do that yet, we google and find this and also this.

One of the answers in the second link gives an extended version of the sr-list command:

xe sr-list uuid=<UUID of SR> params all
uuid ( RO)                    : <UUID of SR>
              name-label ( RW): temporary-sata-disk
[...]
      allowed-operations (SRO): unplug; plug; PBD.create; update; PBD.destroy; VDI.resize; VDI.clone; scan; VDI.snapshot; VDI.mirror; VDI.create; VDI.destroy
[...]
                    VDIs (SRO):
                    PBDs (SRO): <UUID of PBD>
[...]

This shows a lot of stuff, in particular it shows a list of allowed operations and a list of VDIs and PDBs currently connected to the Storage Repository. In the case above, we can see, that there are no VDIs connected to it and one PDB. So we follow the instructions in the first link:

xe sr-list name-label=temporary-sata-disk
uuid ( RO)                : <UUID of SR>
          name-label ( RW): temporary-sata-disk
    name-description ( RW): 
                host ( RO): xenserver1
                type ( RO): lvm
        content-type ( RO): user

which gets us the UUID of the SR (OK, we already had that one)

xe pbd-list sr-uuid=<UUID of SR>
uuid ( RO)                  : <UUID of PBD>
             host-uuid ( RO): 78059c4a-73f2-4975-936a-537529772d67
               sr-uuid ( RO): <UUID of SR>
         device-config (MRO): device: /dev/sdb
    currently-attached ( RO): true

which gets us the UUID of the PDB (we already had that one too)

xe pbd-unplug uuid=<UUID of PBD>

followed by

xe sr-forget uuid=<UUID of SR>

After that last command, the Storage Repository vanishes from XenCenter. Also

xe sr-list

no longer lists it. So I guess, it’s safe now to

  • Shut down the computer
  • Remove the hard disk that was used for that Storage Repository
  • Turn on the computer again

One last question: What is the difference between the xe commands sr-forget and sr-destroy? My google fu nearly left me here, until I found a link to XenServer Administrator’s Guide – Layer 8 Consulting (PDF!). There, on page 45 it says
Destroying or forgetting a SR
You can destroy an SR, which actually deletes the contents of the SR from the physical media. Alternatively you can forget an SR, which allows you to re-attach the SR, for example, to another XenServer host, without removing any of the SR contents.”
So, there you go.