[CentOS] 3ware disk failure -> hang

[Bryan J. Smith]

Joshua Baker-LePain <jlb17 at duke.edu> wrote:
> I guess it depens on your definition of "trouble".  These
> are benchmarks I ran on this system with the 2 3wares in
> hardware RAID5 and a software RAID0 across them:
>       write   read
>       -----   ----
> ext2    81    180
> ext3    34    222
> XFS    109    213
> That ext3 write speed was something I just wasn't willing
> to live with on a system that used to perform so much
better
> (running RH7.3, hw RAID, and XFS).

That's because the 3Ware Escalade 7000-8000 series only have
1-4MB of SRAM.  The Ext3 journal logic is rather "dumb"
(especially on old kernel 2.4) and bursts _more_ than 4MB at
a time.  As a result, you overflow the small SRAM cache of
the 7000-8000 series, and the XOR stalls.

Newer Ext3 journaling code in newer 2.4/2.6 kernels is a
little better, but I still do _not_ recommend you use RAID-5
on the 7000/8000 series.  I have repeatedly recommended
RAID-10 for 3Ware Escalade 7000-8000 series.

I'm still holding off on recommending the 3Ware Escalade
9500S for RAID-5, although most people are seeing good
performance with the 9.2.1.1 firmware released ~9 months ago.
 The verdict is still out on the far newer 9550SX series
(with PowerPC).

Lastly, and quite repeatedly, the 3Ware card does _not_ offer
hot-swap capability when you use JBOD modes.  I, among
countless others, have been saying this for years.  You have
to use _another_ kernel facility to "hide" the status of the
discs when you're using JBOD modes.


-- 
Bryan J. Smith     Professional, Technical Annoyance                      b.j.smith at ieee.org      http://thebs413.blogspot.com
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*** Speed doesn't kill, difference in speed does ***