Controlling file system space usage

File Services Administration Guide for Hitachi NAS Platform

Version
14.7.x
14.6.x
Audience
anonymous
Part Number
MK-92HNAS006-29

The server can monitor space allocation on a file system and trigger alerts when pre-set thresholds are reached; optionally, users can be prevented from creating more files once a threshold has been reached. Alternatively, the file system can be expanded either manually or automatically while online. The command fs-usage controls the monitoring. See the man pages for details.

Two activities consume system space:

  • Live file system. Refers to the space consumed when network users add files or increase the size of existing files.
  • Snapshots. Refers to consistent file system images at specific points in time. Snapshots are not full copies of the live file system, and snapshot sizes change depending on the live file system. As the live file system uses more space, snapshots use more space, and as the data in the live file system is changed, snapshots require less space.
Note: Deleting files from the live file system may increase the space taken up by snapshots, so that no disk space is actually reclaimed as a result of the delete operation. The only sure way to reclaim space taken up by snapshots is to delete the oldest snapshot.

The server tracks space taken up by:

  • The user data in the live file system
  • The file system metadata (the data the server uses to manage the user data files)
  • Snapshots
  • Entire file system
For each of these slices, both a warning and a severe thresholds can be configured. Although they differ from system to system, the following settings should work in most cases:
Warning Severe
Live file system 70% 90%
Snapshots 20% 25%
Entire file system 90% 95%

When the storage space occupied by a volume crosses the warning threshold, a warning event is recorded in the event log. When the Entire File System Warning threshold has been reached, the space bar used to indicate disk usage turns yellow.

When the space reaches the severe threshold, a severe event is recorded in the event log, generating corresponding alerts. If the Entire File System Severe threshold has been reached, the space bar used to indicate disk usage turns amber.

If file system auto-expansion is disabled, you can limit the growth of the live file system to prevent it from crossing the severe threshold, effectively reserving the remaining space for use by snapshots. To limit the live file system to the percentage of available space defined as the severe threshold, fill the Do not allow the live file system to expand beyond its Severe limit check box on the File System Details page.