CERC 1.5/6ch and high load averages, poor performance

[Neil Jones]

The CERC is supposed to be a rebranded Adaptec 6 channel SATA card (I
don't remember the model number...maybe it starts with 2 and ends in
0).  It uses the aacraid driver.

It's currently got 4 drives (500 Gb), all the same model, in a RAID-5
array.  That array is then managed by LVM under Linux (RHEL 4), and
split into a couple of partitions.  The hardware itself is only about
2 weeks old, and the drives haven't shown any problems when I verify
them in the BIOS (and the raid status appears to be normal when I look
at the disks in AFACLI).

Prior to doing a MySQL load (say), the write performance is 50 Mb/s.
During a MySQL load, the write performance is 2 Mb/s, and the loadavg
shoots to 13.

(Apologies, David, if you get a duplicate message.)

..Neil

On 7/10/06, David Hubbard <dhubbard at dino.hostasaurus.com> wrote:
> I've seen that type of issue on crap 3ware controllers,
> not sure who makes Dell's cerc for sata.  What kind
> of raid have you configured?
>
> David
>
> > -----Original Message-----
> > From: linux-poweredge-bounces at dell.com
> > [mailto:linux-poweredge-bounces at dell.com] On Behalf Of Neil Jones
> > Sent: Monday, July 10, 2006 7:28 PM
> > To: linux-poweredge at dell.com
> > Subject: CERC 1.5/6ch and high load averages, poor performance
> >
> > I have a (new) PowerEdge 1800 with a CERC 1.5/6ch controller.  It has
> > a single 4 volume RAID 5 array, which is also controlled through Linux
> > LVM; the system runs Red Hat Enterprise 4.
> >
> > I've noticed that when any application begins to do a lot of disk I/O
> > (e.g., MySQL), the load on the machine jumps up to a very high number
> > (currently, 13).  The applications themselves use very little memory
> > and there is no swapping going on --- all disk I/O is coming from
> > explicit file I/O from an application. The only processes that seem
> > active are the I/O-heavy application, kjournald, and (oddly) kswapd.
> >
> > Has anybody seen this problem before, and if so, what did you
> > do about it?
> > --
> > ..Neil
> >
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> >
>
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--
..Neil


-- 
..Neil