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[Linux-cluster] Suggestion for journal and RG size for small filesystems



We have a need to create a very small GFS filesystem, as low as on a 512MB disk partition. For a three node cluster ( -j 3) what is the suggested value for Journal size and ResourceGroup size? Obviously I want maximize the usable diskspace while still keeping it safe to operate and get a decent performance.
 
The default gfs_mkfs only leaves about 110 / 512MB volume. Reducing the Journal size from 128M(default) to 32M(min) gives me back about 288MB. 

What is the impact of reducing journal size? Can I safely live with this journal size if my app using this filesystem is less metadata intensive?
 
Similarly w.r.t ResourceGroup size, what is the impact of reducing its size from 128M (default) to 32M (min) ?
 
Appreciate any thoughts on this.
 
thanks,
Sridharan
 
 
PS: Few of those gfs_mkfs snippets for reference,
 
$ gfs_mkfs -p lock_dlm -t alpha:gfs2 -j 3 /dev/hda12
...
Blocksize:                 4096
Filesystem Size:        28164
Journals:                   3
Resource Groups:     8
 
$ gfs_mkfs -p lock_dlm -t alpha:gfs2 -j 3 -J 32 /dev/hda12
...
Blocksize:                 4096
Filesystem Size:        101892
Journals:                   3
Resource Groups:     8
$ gfs_mkfs -p lock_dlm -t cisco:gfs2 -j 3 -J 32 -r 32 /dev/hda12
...
Blocksize:                 4096
Filesystem Size:        101868
Journals:                   3
Resource Groups:    14
 
 

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