Re: fragmentation question

[Brady Chang <bchang@xxxxxxxxxxxxx>]

thanks guys for the feedback.
iostat shows balanced io between two filesystems.
testing with RHEL 54, no issues there. seems to be happening on RHEL 55 only.
I do not have the latest 55 kernel. I'm going to upgrade to the latest 55 kernel and rerun the test.



On 9/9/10 7:12 AM, "Eric Sandeen" <sandeen@xxxxxxxxxxx> wrote:

> Brady Chang wrote:
> > Hello All,
> > I have an issue with fragmentation on a particular device
> > thanks for any advice.
> >
> > -Brady
> >
> > I have a Dell r510 with 12 disks
> > 2xraid 5 (6 disks each)
> > raid group1:
> > 48 GB   carved out for os mounted as /
> > remaining space  2.7 TB for xfs mounted as /data1
> > raid group2:
> > 48 GB  for swap
> > remaining space 2.7 TB for xfs mounted as /data2
> >
> > The strange thing is that /data1 never gets fragmented where as /data2
> > is badly fragmented.
> > I believe increase allocsize would help, but not sure how to explain why
> > /data2(/dev/sdd) always gets fragmented and not /data1(/dev/sdb)
> >
> > It's a data warehouse application.  the I/O is balanced between /data1
> > and /data2:
> > output of xfs_db
> > [root@sdw4 data1]# xfs_db -c frag -r /dev/sdb
> > actual 14353, ideal 13702, fragmentation factor 4.54%
> > [root@sdw4 data1]# xfs_db -c frag -r /dev/sdd
> > actual 408674, ideal 13719, fragmentation factor 96.64%
>
> so each file has 30 extents on average (actual/ideal)
>
> > df output
> > /dev/sdb              2.7T  967G  1.8T  36% /data1
> > /dev/sdd              2.7T  1.1T  1.7T  39% /data2
>
> 1.1T/408674 extents is ~3M per extent, not so good.
>
> How many files are on each fs?
>
> > LABEL=/data1        /data1     xfs
> >     allocsize=1048576,logbufs=8,noatime,nodiratime 0 0
> > LABEL=/data2        /data2     xfs
> >     allocsize=1048576,logbufs=8,noatime,nodiratime 0 0
>
> Everything but the first option is default, BTW.
>
> Is xfs_info output on the 2 filesystems the same?
>
> Otherwise Emmanuel's idea is a good one, maybe it's not
> as balanced as you think it is, or maybe they have aged
> differently and have different amounts of freespace
> (see the freesp command in xfs_db)
>
> > By the way, the os is RHEL 5.5 kernel 2.6.18-194.11.1.el5
>
> Was Red Hat support not helpful?
>
> -Eric