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GCS>Sun Microsystems>Storage - Disk>Network Attached Storage
 

Symptoms:

• mistakenly modified file
• mistakenly deleted file
• backups unstable
• Performance issues
  

Purpose/scope:

A checkpoint is a virtual read-only copy of a file volume. While the file volume remains in read/write operation, all data existing at the time the checkpoint was created remains available. Checkpoints are used to retrieve mistakenly modified or deleted files and to stabilize backups.

The checkpoint feature, like all other system processes, takes some system resources away from file service. This document explains how to examine the schedule and space used to minimize this impact. The primary purpose of this document is to help users avoid unintended large allocations of disk space

The amount of space used depends on the number of disk blocks modified since the first active checkpoint was taken. Therefore, managing the changes while checkpoints are enabled and limiting retention time are the best strategies to manage the amount of space used.

If there are any extremetly large deletes done, for example, a complete reconfiguration or the end of a large project, it would be best to disable checkpoints before the delete (which deletes all checkpoints) and enable them again once complete.

For retention time, it is best to keep the maximum retention time as low as possible, and rely on backups for recovery of older data. Most manually created checkpoints are not deleted automatically, so if one is created and forgotten, it could easily take a lot of disk space over time.

To determine the amount of space used by checkpoints for a particular volume, use the chkpntls command. The following is sample output:

NAS > chkpntls vol1 

                             Pseudo-Volume  Num
Volume      Enable  Enab Vis Man   Chkp   Disk Used
/vol1       Yes     Yes  Yes No    7      8.144G

CPID     Created                  Status  Checkpoint
00000600 Wed May 15  9:26:15 2007 Active  backup
00000201 Wed May 16 18:00:00 2007 Active  20070116-180000,14d2h
00000800 Wed May 16 10:40:05 2007 Active  test
00000800 Wed May 16 10:40:05 2007 Active  20070116-104005,14d2h
00000A1A Mon May 14 14:00:00 2007 Delete  backup
0000061B Fri May 11 00:00:00 2007 DelPend backup

In the output above, the key statistic is "Disk Used". This should be checked against the total volume space to ensure a disproportionate amount of space is not being used to store deleted blocks.

The checkpoint name, in the far right column, gives an indication of the type of checkpoint. The scheduled checkpoints created by the system have the long numerical names consisting of the date and retention time, checkpoints created by the NDMP backup software are named "backup", and checkpoints with other names have been manually created.

The status field shows the status of each checkpoint. "Active" means that the checkpoint is still active and usable, and "Delete" and "DelPend" are in the process of being deleted. Checkpoints are deleted with a very low priority, to avoid creating a heavy load on the system. It is not unusual for a heavily checkpointed or otherwise busy NAS system to have many checkpoints in the process of being deleted.

You can delete a single checkpoint with the CLI chkpntrm command. The syntax is chkpntrm volume checkpointname. If this is being done to free disk space, delete the oldest checkpoint first, deleting newer checkpoints will not free disk space.

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