XenServer error SR_BACKEND_FAILURE_44 (insufficient space) explained
Update: Alike's Q-Hybrid backup technology does not use XenServer snapshots, and therefore is not effected by this problem. For more information on Q-Hybrid backups, please refer to the following KB article.
Alike's Enhanced Backups makes use of XenServer's snapshot features in order to provide seamless, zero downtime backups. However, during an Alike Job, you may experience an error during a backup job with the message "SR_BACKEND_FAILURE_44 insufficient space". This simply means that XenServer was unable to create a snapshot for the VM because your Storage Repository didn't have enough space. The process of snapshotting does take additional overhead on your SR, so you do need sufficient room to perform the operation. The specific mechanics of how snapshots work can be found in the Citrix document CTX122978, Understanding Snapshots.
Please note, this error is often associated with Citrix's well known snapshot space reclaim issue. If you are affected by this problem, your would see utilization on your SR that adds up to more than the total of your visible vDisks. Due to this, you would expect to have more space available than you actually do on your SR, which could cause your snapshots to fail. Citrix has provided a work-around, called Leaf Coalesce, or Coalescing, which Alike is able to automate for you. This can provide an effective means for keeping this unreclaimed space issue at bay.
Please refer to the Alike KB article outlining the usage of our leaf coalesce options.
Citrix: Understanding Snapshots
Automating VM Leaf Coalescing with QuorumSoft Alike