Xen VM Snapshots Test
XenServer provides a convenient snapshotting mechanism that can take a snapshot of a VM storage and metadata at a given time. Where necessary, IO is temporarily halted while the snapshot is being taken to ensure that a selfconsistent disk image can be captured. Snapshot operations result in a snapshot VM that is similar to a template. The VM snapshot contains all the storage information and VM configuration, including attached VIFs, allowing them to be exported and restored for backup purposes.
Though snapshot files are small in size initially, they will grow as writes are made to the VM’s disk files. If the number and size of the snapshot files grow significantly over time, they might end up eroding considerable storage space, thereby choking VM operations. To conserve space, administrators need to continuously track snapshot growth per VM, identify ‘heavy-weight’ snapshots that may not be of use any longer, and purge them. The Xen VM Snapshots test helps administrators achieve the same. While the measures reported by the test capture the snapshot file count per VM and the total size of the snapshot files of a VM, the detailed diagnosis reveals the size of each snapshot, thus enabling administrators to quickly spot those snapshot files that are too large in size.
Target of the test : A XenServer host
Agent deploying the test : An internal/remote agent
Outputs of the test : One set of results for each VM on the target XenServer host
Configurable parameters for the test
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Measurements made by the test
Measurement | Description | Measurement Unit | Interpretation |
---|---|---|---|
Number of snapshots: |
Indicates the number of snapshot files of this VM that are currently available. |
Number |
A number of snapshots of a VM provides administrators with multiple restore points. On the flipside though, a high number of snapshots can also be considered a waste of valuable disk space, especially if many of the snapshots hold less critical, but heavy-weight changes/writes to the disk. To accurately identify those snapshots that are consuming disk space excessively, and to learn when they were created, who their parents are, and their current consistent file system state, use the detailed diagnosis of this measure. |
Aged snapshots count: |
Indicates the number of snapshots that are of an age over the configured AGELIMIT. |
Number |
Use the detailed diagnosis of this measure to identify the old snapshots, so that you can figure out whether they deserve to be retained or not. While many snapshots provide essential restore points for VMs, many others hold less critical information. The 'less useful' snapshots can be eliminated to save disk space. |
Large snapshots count: |
Indicates the number of snapshots that are of a size more than the configured SIZELIMIT. |
Number |
Though small in size initially, snapshots can grow with time, but can never grow beyond the original disk file size. If a marked increase is noticed in the value of this measure over time, it could indicate that a number of snapshots are rapidly growing in size. To know which snapshots are growing beyond the size limit set, use the detailed diagnosis of this measure. |
To accurately identify those snapshots that are consuming disk space excessively, and to learn when they were created, who their parents are, and their current consistent file system state, use the detailed diagnosis of the Number of snapshots measure.
Figure 1 : The detailed diagnosis of the Number of snapshots measure