Moving free space between storage pools

Storage Subsystem Administration Guide for Hitachi NAS Platform

Part Number

You can move free space between storage pools that reside on the same HDP pool; however, before starting, consider the strong performance impacts.

The span-list -s command shows:

  • The amount of vacated space on each HNAS stripeset
  • The HDP pool that hosts the stripeset
  • Other spans that share the HDP pool
Use the span-list -s command to determine how much space can be moved to other spans on the same HDP pool. If you recently deleted a file system and see less vacated space than expected, use the span-list-recycle-bin command to identify any file systems that have recently been deleted and still occupy space. To recycle these file systems, use the filesystem-recycle command, which makes it impossible to un-delete the file systems you specify on the command line.

The span-unmap-vacated-chunks command launches a background thread that may run for seconds, minutes, hours, days, or even months. See the man page for commands that monitor and manage its progress.

The free space on the DP pool continues increasing while this background thread runs.

In configurations where the storage has to zero-initialize (overwrite with zeros) HDP pages before they can be re-used, the free space on the pool may continue to increase even after the unmapping thread terminates.

The performance of all DP pools on the affected system are lower than usual until free space has finished increasing, but DP pools on other storage systems are unaffected.