Suboptimal performance due to updates made on a file system or fileset with snapshot

If a file is modified after its snapshot creation, the system can face performance degradation due to the copy-on-write property enforced on updated data files.

Problem identification

Updating a file that has a snapshot might create unnecessary load on a system because each application update or write operation goes through the following steps:
  1. Read the original data block pertaining to the file region that must be updated.
  2. Write the data block read in the step 1 above to the corresponding snapshot location.
  3. Perform the application write or update operation on the desired file region.

Issue the mmlssnapshot to verify whether the snapshot was created before the file data update operation.

In the following sample output, the gpfs2 file system contains a snapshot.

# mmlssnapshot gpfs2
Snapshots in file system gpfs2:
Directory                SnapId    Status  Created
snap1                    2         Valid   Mon Jan 25 12:42:30 2016

Problem resolution and verification

Use the mmdelsnapshot command to delete the file system snapshot, if it is no longer necessary. For more information on the mmdelsnapshot command, see the mmdelsnapshot command.