Ext3 and 3ware RAID5

[Alex Bligh]

--On 15 April 2006 07:33 -0400 Joshua Baker-LePain <jlb17 at duke.edu> wrote:

>> No idea, but I suffer the same problem with a 9550SX-4 with SATA3
>> drives. I don't think ext3 is the problem as dd gives much the same
>> behaviour (you might want to try it). My reluctant conclusion is
>> that the 9550SX is just dog slow, which is why the drives are currently
>> sitting idle. I would love someone from 3ware to disprove this.
>
> When ext2 is almost 2X faster than ext3 at writing, it points pretty
> firmly at something in the journaling code (IMO).  And a journaling FS
> can do decently with this hardware, as XFS also gets ~300MB/s writing.

Sorry forgot to address that point. Writes seem to be especially slow
(there is/was some stuff on the 3-ware site saying slow writes under Linux
were a known problem). I am presuming that ext3 simply does more writing
(even if the extra writes are small and discontiguous but numerous) than
ext2 due to journalling, and this shows up the poor performance.

You might run some benchmarks on the raw partition and see just how
slow writes are. You might also take a look at the 3ware site as I
think there might have been some tuning options they suggested which
allegedly improved things (I gave up) - stripe size comes to mind.

Anyway, do let me know if you find the answer...

Alex