Tag Archives: Xenserver

Virtualization

Create local storage in Xenserver

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For some reason the default installation of Xenserver on one of my machines did not create a local storage repository. I think it might be due to my having installed over an existing installation of Xenserver and the installer got confused.

I tried manually creating a storage repository by running the following command:

xe sr-create content-type=user device-config:device=/dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3 host-uuid=9f8ddd87-0e83-4322-8150-810d2b365d37 name-label="Local Storage" shared=false type=lvm

Alas, it resulted in an error:

Error code: SR_BACKEND_FAILURE_55
Error parameters: , Logical Volume partition creation error [opterr=error is 5],

After much googling I came across this page, which has the explanation. Apparently you need to create an LVM physical volume on the desired partition by running the following command:

pvcreate /dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3

WARNING: software RAID md superblock detected on /dev/disk/by-id/scsi-SATA_WDC_WD3200AAJS-_WD-WMAV2C718714-part3. Wipe it? [y/n] y

It seems the installer noticed an md superblock on this partition and freaked out, hence no local storage. Agreeing to wipe it created the storage repository. One last step: making it the default repository:

xe pool-param-set uuid=<pool UUID> default-SR=<SR UUID>

You can get the pool UUID by running: xe pool-list

Done.

Edit: 10/09/2014

I recently came across a new error message when trying to add a local repository:

The SR operation cannot be performed because a device underlying the SR is in use by the host.

Google searches didn’t reveal much. After a while I realized what was wrong: I had omitted the host-uuid: option. This option is required when you are a part of a pool, but not when you have a standalone xenserver. So, if your xenserver is a member of a pool, don’t forget the host-uuid parameter.

Virtualization

Manually apply patches to Citrix Xenserver

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Citrix Xenserver has many features, all of which are now free as of Xenserver 6.2. XenCenter, however, still expects a support license to use some of its features. One of those features is applying patches. Fortunately it’s easily done via the command line. Their site has documentation on how to do this. Below are my “cliff notes”

  1. xe patch-upload file-name=<filename>
    Note: .xsupdate is the extension of xenserver updates
  2. Wait a moment, then copy the UUID that it outputs
  3. xe host-list
  4. xe patch-apply uuid=<UUID copied from patch-upload>  host-uuid=<host UUID as out put from xe host-list>

If you’re in a pool, instead of xe patch-apply, you can do xe patch-pool-apply <UUID> to apply the patch to all pool members.

Virtualization

Xenserver and clock drift

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When it comes to a virtual machine’s clock my experience with other virtualization solutions has been that it’s automatically synchronized with the host machine. I didn’t notice until recently that this is not the case with Citrix Xenserver – at least when it comes to PVHVM machines.

I tried installing openntpd on each of my VMs and setting it to my internal NTP server (which in turn synchronizes with the web.) After a few days I was frustrated to see that the servers were still not in sync – some were minutes behind while others were inexplicably minutes ahead. Some of this might have to do with my experiments on live migrating these VMs a while back.

At any rate, it was clear that openntpd failed to do the job. Some research revealed that there is a bug where it reports adjusting the clock when the real status was an error. That little bug cost me an hour or two of digging and troubleshooting. Very frustrating.

I switched to plain old ntp instead and the problem was resolved within moments.

clock

Moral of the story: Make sure you have a proper NTP setup for each of your VMs if you’re going to use Citrix Xenserver.

Virtualization

Migrating a Windows 8.1 VM from Xen to Xenserver

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Since Citrix recently released the entire Xenserver product to the world as free, open source software I thought I might give it a try. I have been pleased with the results and wanted to migrate my desktop VM over to it.

I’ve had a devil of a time getting my Windows 8.1 Professional virtual machine to migrate from plain Xen to Citrix Xenserver 6.2. My first mistake was not doing research before migrating hypervisor environments. While it is true that Citrix uses Xen as the underlying hypervisor, it turns out that there are still plenty of differences between the two environments.

I thought I would take the easy route by installing Citrix Xenconvert and converting my Xen Win8.1 VM to a format Xenserver likes. Although Xenconvert was designed for Physical to Virtual migration, I’ve found in the past that it works just as well for virtual to virtual migration.

After migrating to Xenserver I was greeted with the following friendly message:

INACCESSIBLE_BOOT_DEVICE windows 8.1 bluescreen
lovely

As far as I can tell it was the Xen GPLPV drivers that were the culprit. This leads me to my second mistake: not having a proper backup of the VM. I didn’t keep a backup of this VM in the Xen-friendly format after I migrated it to xenserver. This was mainly due to laziness – a classic example of “one ounce of laziness now produces one ton of hard work later.”

Instead of simply just booting the VM and removing the GPLPV drivers I had to attempt to do it via the Windows PE on the Windows 8.1 disc. I first tried running the GPLPV uninstall script from here, modifying it to point to the c:\ drive for both files and registry settings. Alas, that didn’t appear to do anything.

I then tried to go through the registry via the Windows PE and remove any references to Xen-anything. Success! Or so I thought. It turns out that blindly plowing through the Windows registry without an idea of exactly what you were doing has consequences. The VM would boot but I could not for the life of me get network drivers to work. As far as I can tell I corrupted something in the registry and despite my best efforts I couldn’t fix it.

At this point I had learned to back things up so I kept restoring from backups and messing with removing various registry keys. I continued this trial and error process for some time. After much weeping, wailing, and gnashing of teeth, I finally found the right combination of keys you must remove in order to boot again.

I took what I learned and updated the script from above to make it work with the WinPE environment . Download it here.

Boot into your PE environment of choice and run the script. When it’s finished, your VM will now be able to boot successfully.

The last step is to go into device manager and delete all xen-related drivers, then re-install them. After all that is said and done, your migration from xen to xenserver is complete. Repeat the exact same process to migrate from xenserver back to xen.