Jan 082018
 

Apparently shrinking a Windows VM (actually any kind of VM) cannot be done with XenServer and XenCenter. You need to create an image of the original volume to a smaller virtual disk in order to do that.

On top of that, the tool that used to work fine for this, Citrix XenConvert, has been deprecated by Citrix and is no longer available for download.

And just to make matters worse, this answer on ServerFault links to an article that is no longer available (or did, until I edited it). Fortunately it’s still in the WaybackMachine

Now, where do we get XenConvert? It’s available for download here in various versions. I took version 2.5. and followed the instructions in the above mentioned article. You might want to virus check the installer before running it.

  1. Create a new virtual disk with the desired size.
  2. Attach it to your VM.
  3. Start the VM.
  4. Optionally, shrink the source drive (partition) from within the virtual machine (Windows 7+ comes with the tools for that).
  5. Format the newly created virtual disk.
  6. Install XenConvert
  7. Start XenConvert, select From: Volume and To: Volume (That’s not the default.)
  8. Select source and destination volumes.
  9. Run the conversion (which takes forever).
  10. Activate the new partition in the Disk Manager (if you forget this, you won’t be able to boot from it).
  11. Shutdown the VM.
  12. Detach the original virtual disk.
  13. Boot the VM (from the new virtual disk).

If everything works, you can now delete the original virtual disk.

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.

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.)

There is at least one reason why installing updates for XenServer via XenCenter may fail (with unhelpful error messages of course): You haven’t got created any Storage Repository yet.

One might think that this is pretty unusual but your’s truly has actually managed to run into this problem. Why? Because I didn’t install the drivers necessary for accessing the hardware RAID controller (in my case the LSI megaraid package). Usually you do that during the XenServer setup but I was at that time not aware that I would actually need a driver. And thus apart from the boot disk there was nowhere to put a Storage Repository. And I didn’t want to put that on the boot ssd. So I ended up with a XenServer installation that didn’t have any Storage Repositories.

So, what can you do?

You can attach a single SATA hard disk to the system and configure it as a storage.

One might think that is easy to do using XenCenter since there is a menu entry Storage -> New SR, but no, there you can only add NVS, iSCSI, Hardware HBA or Software FCoE. Local drives aren’t even mentioned.

So you have to resort to the xe command as described here:

  1. Shut down and turn off the computer
  2. Attach the hard disk and boot
  3. On the console use fdisk to get information about the new hard disk
    fdisk -l
    

    Search for the new hard drive in the list. It will be the last on the list and it is indicated as /dev/sdc. c is the position it is in. Generally, it starts at a, and the list continues. You can verify the device path using the SCSI ID in /dev/disk/by-id directory by listing out the contents.
    Note: I wouldn’t rely on the drive being the last one in the list. Definitely verify the drive parameters that fdisk outputs.

  4. Run the following command from the command line interface (in the console or on the a computer with XenCenter installed):
    xe sr-create name-label=<Name of Storage> shared=false device-config:device=<Path of the Storage device> type=lvm content-type=user
    
    • Name of Storage is the name of the Storage Repository you require
    • Path of the Storage device is the path as noted in the preceding tasks, /dev/sdc)
      Now, the installed hard drive is visible in the XenServer Console.

    Note: This works fine if you run it on the server console. If you run it from a remote computer with XenCenter, you need additional parameters to actually connect to the server. In that case insert the following between xe and sr-create:

    -s <server> -u <username> -pw <password>
    
    • server is the server’s name or IP address
    • username is the user to logon (e.g. root)
    • password is the password of the given user

And yes, it worked. After adding this Storage Repository I could install the updates.

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