[CentOS] 3ware 9550 series

David Thompson thomas at cs.wisc.edu
Mon Mar 6 21:56:38 UTC 2006

Troy Engel wrote:
>David Thompson wrote:
>> Peter =?iso-8859-1?q?Kjellstr=F6m?= wrote:
>>> raid5, #2 I can't get good read performance on two raid5s in a lvm stripe).
>> Yeah, we've also seen performance issues with raid5 on the 9500 series 
>> products.  The benchmarks we run look good, but when we've put them into 
>As per an old thread on the list, I have a new 9500S-12 and am seeing 
>the same performance problems. But, I'm fairly sure it's because without 
>the BBU installed write-cache is disabled. I have ordered the BBU and 
>expect here soon, I'll see if I can't post some pre-BBU/write cache and 
>post-BBU/write cache numbers, if I find a good test.

We throw caution to the wind and run write-cache-enabled without a BBU, and 
still see a significant drop in performance compared to raid-1.

>Right now I'm running Arkeia on it as the backup-to-disk, and in the 
>middle of the heaviest use I'm seeing about 50-60% I/O wait, horrible. 
>I'm hoping the write cache is going to help this a lot. (*)

If you throw a sufficiently heavy (and multi-threaded) load at any disk array 
of this type, eventually you can drive a system to I/O-wait.  On our systems, 
we look more at total disk throughput and characterization of workload 
(sequential vs. random access), rather than just I/O wait.


Let me know what you find.  

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