PERC 3/DC - Dual Channel performance

Sigbjorn Strommen sigbjorn.strommen at
Mon Jun 10 12:34:00 CDT 2002

Paco Culebras Amigo wrote:

> Maybe I'm saying something stupid, but :
> I have a PE 4600 (RedHat 7.2) system with a PERC 3/DC and 7 U160 discs,
> having 1 disc in Hotspare and the other 6 in 3 arrays of 2 discs in RAID
> 1, all in the same channel.
> It's possible to increment the performance of the system having 3 discs
> in channel 0 and 3 discs in channel 1 in RAID 1 ?

Well, if you're going from 3 times 2 disks in raid 1 to 2 times
3 disks in raid 1, you will get less disk space available.

In addition, the performance increase in using two channels vs.
one channel is not that great with the PERC's, as they are just
too slow to start with.
I've done tests where I shuffled data between disks on different
channels, and it turned out to be just a few percents faster then
doing the same tests between partitions on one disk...
Even raid 0 across the two channels did not help.

Conclusion is, the PERC's are slow whatever config you are setting
up, and there's nothing you can do about it except for hoping that
future drivers and firmware will help a little (but even so, there's
nothing you can do about the slow processor on the controller).

> Any suggestions/experiences/recommendations in this way and
> PowerEdge/RedHat/Oracle ?

If you search the mail archives you will find discussions about
performance and various opinions on what you should do. IMO there's
no choice but using software raid for performance.  Raid 1 is not
so CPU intensive, so even if you're running databases and other
applications I would *guess* that software raid is faster. (Just
remember that there are some safety advantages to having battery
backed up hardware controllers).

> Is better to install Suse ?

I can't see why that would help on performance. If there's no other
reason why you would prefer Suse you are probably better off staying
with Red Hat.


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