[CentOS] 3ware 9550 series

[Troy Engel]

David Thompson wrote:
> 
> 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.

Well yeah, how on earth can you compare the performance of a raid-5 
array with a raid-1 array? raid-1 write performance is the same as a 
single disk (within reason).

> Let me know what you find.  

The BBU showed up today and managed to charge prior to the arkeia backup 
window so I could turn on write cache. At a glance statistics comparing 
Saturday night to now:

sat:
                   CPU     %user     %nice   %system   %iowait     %idle
08:10:05 PM       all      4.88      0.91      3.16     32.63     58.41
08:20:10 PM       all      6.69      0.43      4.25     44.49     44.15
08:30:09 PM       all      9.95      0.64      5.74     50.90     32.76

now:
                   CPU     %user     %nice   %system   %iowait     %idle
08:10:01 PM       all      1.97      3.64      2.93      9.19     82.27
08:20:01 PM       all      2.62      5.42      4.30     12.79     74.86
08:30:02 PM       all      3.49      3.91      4.82     16.00     71.78

I'd say that was a rather significant increase; it's in no way a formal 
test, but if I see this type of result after a few more nights then I'd 
say the $100 for the BBU to enable write cache safely is money well spent...

-te

-- 
Troy Engel | Systems Engineer
Fluid Inc. | http://www.fluid.com