Re: Is it possible to change sunit of log section post-mkfs

Dave Chinner
2015-11-03T19:11:55Z

On Tue, Nov 03, 2015 at 01:18:53PM +0100, Michael Weissenbacher wrote:
> Hi!
> I have a XFS file system which lies on a 10-disk RAID-6 device that was
> created with Chunk Size = 1MiB.
> On mkfs.xfs time this was - as far as i know - specified with "-d
> su=1m,sw=8".
>
> xfs_info shows the following:
> meta-data=/dev/sdb1 isize=256 agcount=15,
> agsize=268435200 blks
> = sectsz=512 attr=2
> data = bsize=4096 blocks=3905945088, imaxpct=5
> = sunit=256 swidth=2048 blks
> naming =version 2 bsize=4096 ascii-ci=0
> log =internal bsize=4096 blocks=521728, version=2
> = sectsz=512 sunit=8 blks, lazy-count=1
> realtime =none extsz=4096 blocks=0, rtextents=0
>
> Interestingly, the sunit value of the log seems to be incorrect - as it
> should be 256 too, like the sunit value of the data. I am pretty sure
> the reason is that the log sunit cannot be 256 blks (=1024KiB) and
> because of this mkfs.xfs did fall back to the default of 8 blks
> (=32KiB). I found evidence of this in the following thread:
> http://oss.sgi.com/archives/xfs/2012-06/msg00431.html
>
> What i want to achieve is to set the log sunit to the maximum possible
> of 64 blks (=256KiB).

Why? Is there a performance problem with the default setting?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com