The maximum number of Snapshot copies allowed per volume is 255, so it is necessary to create backup policies that optimize space on the volume, and avoid the 255 Snapshot copy limit.
You can conserve space by backing up distinct primary qtrees from multiple storage systems to the same secondary volume at the same time.
Assume that multiple primary storage systems contain qtree1 through qtree5. A backup policy specifies a sequential back up schedule for each qtree, and these qtrees are backed up to qtrees of the same name on the same secondary volume. Five backups are taken of each qtree, which results in five Snapshot copies. Assume these Snapshot copies are named snapshot1 through snapshot5 respectively, and each contains a backup of qtree1, qtree2, qtree3, qtree4, and qtree5.
This policy conserves space because multiple qtrees are backed up at the same time. It is less desirable to set policies that back up single qtrees multiple times because doing so results in more Snapshot copies than necessary.
You can increase Snapshot storage capacity by using FlexVol volumes. FlexVol volumes do not increase the amount of physical storage space, rather they share space within an aggregate with other FlexVol volumes, and each volume supports 255 Snapshot copies.
Assume that qtree1, qtree2, qtree3, qtree4, qtree5, and qtree6 are backed up to the same volume. Qtree1, qtree2, and qtree3 are backed up twice a day, and qtree4, qtree5, and qtree6 are backed up once a day. After five days, there will be a total of ten Snapshot copies on the destination volume.
At the 255 maximum Snapshot copy threshold for the volume, the number of backups stored equals 250 that contain qtree1 through qtree3, and 125 that contain qtree4 through qtree6. While effective, this policy could be more efficient if the data was backed up to multiple FlexVol volumes.
FlexVol volumes are managed separately within the physical resources of your storage system. By increasing the number of volumes within a fixed aggregate, you increase Snapshot storage capacity because each volume maintains a 255 Snapshot copy limitation. FlexVol volumes are extremely efficient for grouping primary qtrees with similar backup schedules.
Assume two FlexVol volumes totaling the same amount of disk space. Qtree1, qtree2, and qtree3 are backed up to one FlexVol volume, and qtree4, qtree5, and qtree6 are backed up to the second FlexVol volume. In this case, the number of backups stored on each FlexVol volume equals 250 with one volume containing qtree1 through qtree3, and the other containing qtree4 through qtree6. The amount of space consumed is the same, but Snapshot storage capacity is optimized.
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Last updated: 01-Dec-2005 16:36:13