PERC 3/DC - Dual Channel performance

Seth Mos knuffie at
Mon Jun 10 16:57:01 CDT 2002

At 23:16 10-6-2002 +0200, Sigbjorn Strommen wrote:
>Don't know why (but that's how I read the original email)...

Or does he mean 3 raid 1 arrays striped/spanned or 2 raid 0 arrays mirrored?

The first works.

>Possibly.  I tried chunksizes 32, 64 and 128, with no differences
>(on real data at least).

The 256K chunk sizes performed well. 128K for the raid 1 volumes and a 
multiple chunk size for the striping raid0 array. It worked reasonably well.

If experts can chime in that would be great. :)

>BTW, I notice you get a lot higher block reads then I did (well, all
>your numbers looks better actually), maybe you need to increase your
>data size a bit (from my tests with bonnie++ it looked like 2 times
>the RAM is not enough)

I can't test anymore. The machine is now running NT4 and exchange server.

>What kind of card is the "LSI logic Megaraid 473"?  I thought the
>PERC 3DC's where the same as the Elite 1600?

Yup, the model number is 473 for the Elite 1600.

> > What I don't understand is that the rewrite speed of raid5 is higher then
> > with hardware raid 10. On both occasions I was using cached IO on the
> > controller and 128KB chunk size.
>Well, that would fit with my results as well.

I'm still not complaining. I have an older megaraid here with 4MB cache 
(it's a 428) which can do about 4MB/s to a raid5 volume and 6MB/s in a 
raid10 volume. (NT4 old exchange server ;)

Which on it's turn is a _lot_ better then the DAC 960 PG with 4MB cache on 
a similar machine and disks as the NT box. This one however only manages 
1MB/s _barely_ if you kick everyone off the box. (NCR MP-RAS SVR4)

The trick is that if you just put in a 39160 (I had a spare lying around) 
and do linux software raid you can reach something like 25MB/s in raid 5 
mode. Not too shabby for a (crappy NCR) dual PII 400

Oh and managing really old raid controllers is a PITA. Software raid is a 
lot easier to manage.


It might just be your lucky day, if you only knew.

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