XenServer Error: SR_BACKEND_FAILURE_44 (insufficient space)

Categories: XenServer, Alike v3, Alike v4


Alike’s Enhanced Backups & Replication make use of XenServer’s snapshot features. However, during an Alike Job, you may experience an error during a backup job with the message “SR_BACKEND_FAILURE_44 insufficient space,” or “Insufficient space in target SR.”

This simply means that XenServer was unable to create a snapshot for the VM because your Storage Repository didn’t have enough space. This can sometimes be confusing when your SR looks like it has enough space available.


The process of snapshotting in XenServer can take more storage space on your SR than you might expect, depending on your version of XenServer. For more details on the process, the specific mechanics of how snapshots work can be found in this Citrix document on Understanding Snapshots.

Please Note: This issue is limited to the XenServer platform, and has been greatly minimized in more modern versions of XenServer (6.2+). Hyper-V enhanced backups/replication are not affected, nor are any of Alike’s Q-Hybrid based operations, as they strictly utilize VSS for their snapshotting needs.

Final Notes

*Please Note: Alike’s Q-Hybrid backup technology does not use XenServer snapshots, and therefore is not affected by this problem. For more information on Q-Hybrid backups, please refer to the following KB article.

If you are still receiving this XenServer error code after troubleshooting, please open a support ticket. See the KB article, “How to Use Quadric Support,” for instructions on how to open a ticket.

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