[Linux-cluster] GFS2 file system maintenance question.

[yue]

1.
GFS2 is based on a 64-bit architecture, which can theoretically accommodate an 8 EB file system. However, the current supported maximum size of a GFS2 file system is 25 TB. If your system requires GFS2 file systems larger than 25 TB, contact your Red Hat service representative.





At 2011-03-15 06:35:30，"Jack Duston" <jduston at ll.mit.edu> wrote:

>Hello folks,
>
>I am planning to create a 2 node cluster with a GFS2 CLVM SAN.
>The following Note in the RHEL6 GFS2 manual jumped out at me:
>
>Chapter 3. Managing GFS2
>Note:
>Once you have created a GFS2 file system with the mkfs.gfs2 command, you 
>cannot decrease the size of the file system. You can, however, increase 
>the size of an existing file system with the gfs2_grow command, as 
>described in Section 3.6, “Growing a File System”.
>
>This seems to me to make a GFS2 LV un-maintainable.
>
>What concerns me is the issue of how to remove a LUN from the GFS2 LV. 
>This will be a necessity *when* there are hardware problems with a 
>storage unit, End of Life/obsolescence (a la XRaid), or upgrade (replace 
>1TB HDDS with 3 TB HDDs in the LUNs).
>
>Hardware does not last forever, and manufacturers do EOL products or go 
>out of business.
>I had also hoped to upgrade the 1TB HDDs in our current LUNs with 3 TB 
>HDDs next year.
>
>I planned to free up enough space on the GFS2 LV to migrate data off one 
>LUN. I could then decrease the GFS2 file system size, remove the LUN 
>from the LV, destroy the RAID LUN, replace 1TB HDDs with 3TB HDDs, 
>rebuild the RAID LUN, add the new larger LUN to the LV, increase the 
>GFS2 file system size, and repeat migrating data off the next LUN.
>
>If the above note is correct, it seems to only way to deal with a 
>hardware issue, obsolescence/EOL, or upgrading components is to destroy 
>the entire GFS2 file system, build a new GFS2 file system from scratch, 
>and restore data from backups. This might not be too bad with a small 
>SAN of 20TB, but our data will exceed 100TB and it would be good not to 
>have to rebuild Rome in a day.
>
>Can anyone confirm that GFS2 file system cannot be decreased? If so, is 
>there any plan to add this capability/fix this issue in a future 
>release? Is there another/better way to remove a LUN from GFS2 than what 
>I considered?
>
>Any info greatly appreciated.
>
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