[Lustre-discuss] Reclaiming Reserved Disk Space

Andreas Dilger andreas.dilger at oracle.com
Thu Nov 25 15:57:00 PST 2010


On 2010-11-25, at 13:12, Wojciech Turek wrote:
> I forgot to ask, is setting reserved % to 0 is safe on Lustre filesysytem?

It is safe, but can lead to serious (and permanent) fragmentation of the filesystem, which can lead to permanent performance loss.  Consider reducing it to some smaller fraction than 5%, but leaving some reserve.

> On 25 November 2010 19:15, Wojciech Turek <wjt27 at cam.ac.uk> wrote:
>> I am trying to reclaim the default 5% of reserved disk space on Lustre filesystem following procedure describe in the Lustre manual (chapter 23.3.10). File system is in use and I would like to avoid any downtime. 
>> 
>> [root at oss17 ~]# tune2fs -m 1 /dev/sdg
>> tune2fs 1.41.12.2.ora1 (14-Aug-2010)
>> tune2fs: MMP: device currently active while trying to open /dev/sdg
>> 
>> I understand it is the MMP flag which prevent tune2fs to access the device, is there a way to work around this or is my only option to umount OSTs (eek, downtime)

It should be possible to do this with a modification to tune2fs.

The issue is that this operation is only safe on a mounted filesystem if it is a local mount, and not a remote mount.  tune2fs probably needs to skip the MMP checking in this case, but it needs to check that the filesystem is mounted locally.
 
Cheers, Andreas
--
Andreas Dilger
Lustre Technical Lead
Oracle Corporation Canada Inc.




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