XFS: Abysmal write performance because of excessive seeking (allocation groups to blame?)

[Stan Hoeppner]

On 4/10/2012 9:02 AM, Stefan Ring wrote:
>> And is XFS aligned to the RAID 6?
>>
>> What does xfs_info display on it?
> 
> Yes, it’s aligned.
> 
> meta-data=/dev/mapper/vg_data-lvhome 

Is the LVM volume aligned to the RAID stripe?  Is their a partition atop
the RAID LUN and under LVM?  Is the partition aligned?  Why LVM anyway?

>                                  isize=256    agcount=4, agsize=73233656 blks
>          =                       sectsz=512   attr=2
> data     =                       bsize=4096   blocks=292934624, imaxpct=5
>          =                       sunit=8      swidth=32 blks
> naming   =version 2              bsize=4096   ascii-ci=0
> log      =internal               bsize=4096   blocks=143040, version=2
>          =                       sectsz=512   sunit=8 blks, lazy-count=1
> realtime =none                   extsz=4096   blocks=0, rtextents=0
> 
> I changed the stripe size to 32kb in the meantime. This way, it
> performs slightly better.

The devil is always in the details.  Were you using partitions and LVM
with the RAID1 concat tesing?  With the free space testing?

I assumed you were directly formatting the LUN with XFS.  With LVM and
possibly partitions involved here, that could explain some of the
mediocre performance across the board, with both EXT4 and XFS.  If one
wants maximum performance from their filesystem, one should typically
stay away from partitions and LVM, and any other layers that can slow IO
down.

-- 
Stan