Bug 163823 - gfs_tool reclaim explanation
gfs_tool reclaim explanation
Product: Red Hat Cluster Suite
Classification: Red Hat
Component: gfs (Show other bugs)
All Linux
medium Severity medium
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Assigned To: michael conrad tadpol tilstra
GFS Bugs
Depends On:
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Reported: 2005-07-21 10:05 EDT by Bastien Nocera
Modified: 2010-01-11 22:06 EST (History)
1 user (show)

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Doc Type: Bug Fix
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Last Closed: 2005-07-27 15:31:14 EDT
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Description Bastien Nocera 2005-07-21 10:05:35 EDT
Using GFS on a 4 node cluster. In a regular base we run into the problem where a
large amount of the available storage is used in meta data.

For example on this partition
/dev/pool/gpo_worko    17G  7.0G  9.3G  43% /worko

And a 100MB file could not be written.

The problem goes away as soon as 'gfs_tool reclaim' is issued.

There is not a single usage pattern, it varies from 100000s of small files,
which are written and deleted a couple times a second, up to a 1TB file, that is
written, and sometimes deleted.

Questions are:
- is the behaviour supposed to be like this?
- if it is, is it planned to change it?
- is it recommended to run "gfs_tool reclaim" every couple of hours through cron?
Comment 1 michael conrad tadpol tilstra 2005-07-27 15:31:14 EDT
gfs grabs free blocks as needed and makes them into meta-data blocks.  Once a
block is marked as meta-data, it remains as meta-data even if it isn't being
used.  gfs_tool reclaim can be used to convert these back.  Doing so locks the
entire fs while the reclaim takes place.  The reason for keeping meta-data
blocks around like this is a bit of a kludge to deal with the way nfs server is

From the above, the best responses are (one of these should be enough.)
- Change the usage pattern
- If the work load is from some kind of batch system, add gfs_tool reclaim to
part of the batch job.
- create two seperate filesystems, one for the tiny files, one for the larger.
- create a single fs that is large enough that it can have all of the unused
meta-data and large files.

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