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Volume Snapshot auto delete

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Category:
data-ontap-8
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core
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Applies to

  • Product Model: FAS3140-R5
  • OS: Data ONTAP 8.1.2P2 7-Mode

Issue

Volume snapshot is auto-deleted even though snapshot retention currently is set for 30 days.
============
Snapshot autodelete settings for AUHVSNA1_SHARED:
                                        state=on
                                        commitment=try
                                        trigger=snap_reserve
                                        target_free_space=10%
                                        delete_order=oldest_first
                                        defer_delete=user_created
                                        prefix=(not specified)
                                        destroy_list=none =========================================
00000011.0010da6a 1b4cc5ac Tue Nov 25 2014 00:56:12  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'weekly.0' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da6c 1b4cc63c Tue Nov 25 2014 00:56:27  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'hourly.4' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da6e 1b4cc6d1 Tue Nov 25 2014 00:56:42  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'hourly.3' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da70 1b4cc758 Tue Nov 25 2014 00:56:55  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'hourly.1' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da72 1b4cc7f1 Tue Nov 25 2014 00:57:11  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'hourly.0' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da74 1b4cc888 Tue Nov 25 2014 00:57:26  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'nightly.0' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da76 1b4cc937 Tue Nov 25 2014 00:57:43  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'Dont_Delete_INC0752286' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da79 1b4cc9ab Tue Nov 25 2014 00:57:55  11:00 [disk.healthTrigger:warning] Disk 3a.42 received NHT health trigger (0x1 0xb 0x5d 0x5)
00000011.0010da7a 1b4cc9e9 Tue Nov 25 2014 00:58:01  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'Snapshot_4:45_24_11_2014' in volume 'AUHVSNA1_SHARED' to recover storage
00000011.0010da7c 1b4ccaa3 Tue Nov 25 2014 00:58:20  11:00 [wafl.volume.snap.autoDelete:info] Deleting snapshot 'Manual_snapshot' in volume 'AUHVSNA1_SHARED' to recover storage

As you can see here, On Nov 23, the volume /vol/AUHVSNA1_SHARED/ was at 96% capacity.  Something happened between Nov 23, and Nov 25 that pushed that volume to its capacity and snapshots were deleted on Nov 25 to save the volume.

Filesystem                         kbytes           used              avail    capacity  Mounted on
Nov 23
/vol/AUHVSNA1_SHARED/                               5653468812                 5424660856                  228807956      96%  /vol/AUHVSNA1_SHARED/
/vol/AUHVSNA1_SHARED/.snapshot             115376912                    87988840                      27388072      76%  /vol/AUHVSNA1_SHARED/.snapshot

Nov 25
/vol/AUHVSNA1_SHARED/                              5858989708                 5452568432                  406421276      93%  /vol/AUHVSNA1_SHARED/
/vol/AUHVSNA1_SHARED/.snapshot             119571216                    2969476                         116601740       2%  /vol/AUHVSNA1_SHARED/.snapshot
====================================================

The oldest snapshots were deleted first as the options dictated, but in order to keep the volume alive, it kept deleting snapshot due to space issues, that is, the volume, being at 96% capacity, ran out of space and the snapshots kept deleting until space was sufficient. 

Something happened at that time to push the volume to capacity, and all snapshots were deleted. The delete process would have stopped at one snapshot if volume space permitted; however, the volume space did not permit. 

Also, the target_free_space is set to 10%, see Deleting Snapshot copies automatically

target_free_space: Determines when to stop deleting Snapshot copies. The target_free_space value is some percentage of the volume. For example, if you specify 20, then snapshot copies are deleted until 20% of the volume is free space.

It is a common practice to specify the target_free_space value 2% less than the auto-delete threshold to avoid deleting snapshot copies unnecessarily.

 

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