[lustre-discuss] Recommended minimal amount of free space to keep on a lustre filesystem

[Andreas Dilger]

On Jul 23, 2018, at 07:48, H. Meijering <h.meijering at rug.nl> wrote:
> Is there a recommended  amount of free space to keep fere on a Lustre file system.
> We kept always 80% in but with the growing volumes it's starting to become very expensive to keep 20% free on big sized file-systems.
> 
> Are there recommendations for Lustre file-systems to keep a amount free of disk-space, to keep performance and stability in a good health for lustre?

This depends on your workload and how long the files live in your filesystem.

If you have large numbers of large parallel file writes, then having more free space ensures that the filesystem does not get too fragmented.  If there are fewer, sequential or small file writes, but large numbers of readers (e.g. AI/Genomics) then possibly having less free space is OK.

Having at least a few hundred GB free on each OST is recommended, but these days that may only be 5% of the filesystem size.

The other factor is that disks can be up to 50% slower when the inner tracks (higher block numbers) are used compared to the outer tracks (lower block numbers), because of the changing linear velocity of the tracks moving under the drive read/write heads.  Keeping the filesystem less full uses the higher block numbers less.

Cheers, Andreas
---
Andreas Dilger
Principal Lustre Architect
Whamcloud







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