PERC 3/DC - Dual Channel performance

Seth Mos knuffie at xs4all.nl
Mon Jun 10 14:52:00 CDT 2002


At 19:32 10-6-2002 +0200, Sigbjorn Strommen wrote:
>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.

3 disks in raid 1 ???
Or 2 disks in raid1 with one hot spare.

>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.

I did some bonnie++ benchmarks with software raid10 vs hardware raid10. The 
biggest jump is in the rewrite speed. And larger chunks then 128K also help 
a lot.

Dell PowerEdge 2550, 2GB  ram, dual 1,4Ghz PIII, 4 18GB 10K rpm disks, 
split backplane (2 disks/channel).
LSI logic Megaraid 473, 2 channel, u160 128MB battery backed cache, write 
back, 128KB chunk, cached IO.
Software raid tested on onboard AIC7xxx on seperate channels.

ext3, hardware raid 10, 10GB partitie, 2GB ram, dual 1,4 PIII
Version  1.02       ------Sequential Output------ --Sequential Input- --Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
zwelgje.coltex.n 4G 17095  93 32641  24 18311  15 16649  90 117731  31 
464.0   1
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec 
%CP  /sec %CP
                  16  1743  97 +++++ +++ +++++ +++  1882  99 +++++ 
+++  8030  99

ext3, software raid 10 128k/256k chunk size
Version  1.02       ------Sequential Output------ --Sequential Input- --Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
zwelgje.coltex.n 4G 16608  98 58473  64 29592  30 17750  98 126850  43 
446.6   1
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec 
%CP  /sec %CP
                  16  1723  97 +++++ +++ +++++ +++  1783  99 +++++ 
+++  7050 100


>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).

You will especially notice this with raid 5 if you have a lot of disks.
The controller can handle 4 disks just fine but software raid is already 
showing it's faster in most respects.
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.

ext3, hardware raid5, 2GB ram, dual 1,4 PIII
Version  1.02       ------Sequential Output------ --Sequential Input- --Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
zwelgje.coltex.n 4G 17429  96 41230  31 21179  18 16387  88 98119  25 426.0   1
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec 
%CP  /sec %CP
                  16  1578  92 +++++ +++ +++++ +++  1683  99 +++++ 
+++  6542  99

ext3, software raid5, 2GB ram, dual 1,4 PIII
Version  1.02       ------Sequential Output------ --Sequential Input- --Random-
                     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- 
--Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
zwelgje.coltex.n 4G 16556  99 52272  50 27639  39 17769  99 126508  50 
408.0   3
                     ------Sequential Create------ --------Random 
Create--------
                     -Create-- --Read--- -Delete-- -Create-- --Read--- 
-Delete--
               files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec 
%CP  /sec %CP
                  16  1700  97 +++++ +++ +++++ +++  1817  98 +++++ 
+++  6653  97


Cheers

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




More information about the Linux-PowerEdge mailing list