[Lustre-discuss] Reclaiming Reserved Disk Space

[Wojciech Turek]

Thanks for your reply Andreas. I have one more question regarding the size
of the reserved space. Our average file size is 1MB, OST size is 7.2TB and I
am planning to set reserved space to 0.15% which  will give us 12GB per OST.
Would you agree that this is enough to keep fragmentation low?

Best regards,

Wojciech

On 25 November 2010 23:57, Andreas Dilger <andreas.dilger at oracle.com> wrote:

> 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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