[CentOS] question on RAID performance

Fri Apr 11 04:13:41 UTC 2008
Guy Boisvert <boisvert.guy at videotron.ca>

John J. Lee wrote:
> On Thu, Apr 10, 2008 at 6:43 PM, Jerry Geis <geisj at pagestation.com> wrote:
>> Hi all,
>>  I was wonder what experiences there are out there with using RAID-X for
>>  performance increases. I do use RAID-1 (2 disks) but am interested in
>>  attemtps to gain higher R/W performance. Do the RAID-5's etc give
>> noticeable
>>  performace increases?
>>  A significant help for me was using ccache for compiling programs. That was
>>  a real performance increase.
>>  Thanks for any suggestions/opinions.
>>  jerry
 > If you want to higher R/W performance, you should go for raid0.
 > raid0 fragments the data into the number of disks and distributes them.
 > It gains a big performance.  One drive fails, however, all data gone.
 > raid5's benefit is not the speed but the effective space usage with
 > the least data redundancy.
 > Bitwise parity calculation consumes lots of processing power.  So
 > raid5 is the least choice in terms of performance.
 > -john

I had about the same interrogation a couple of months ago.  I had to 
upgrade a mail server that was using a single IDE drive to store about 
90 Gigs of mail, served by Communigate Pro on CentOS 4.6 (32 bits).  The 
server was starting to crawl with high %iowait.  The drive was simply a 
regular Western-Digital 7200 RPM 200 Gigs drives.  Imagine the random 
access load, which is simply too much for a drive which is designed to 
handle single user load.

I finally set for 4 x Seagate SAS 73 Gigs 15000 RPM on RAID 10.  The 
performance is very good.  About 150-160 MiB/s througput R/W.  We use an 
Adaptec 3405 (Unified SAS/SATA Crontroller, CentOS stock drivers) on a 
new Tyan Transport TA26 (B3992-E), 4 Gig RAM, Opteron 2214 & CentOS 5 

I made tests with the same server in RAID 5.  Read throughput was about 
the same but write was slightly lower (XOR Calculation) at about 135 
MiB/s which is still real good.  I chose RAID 10 because i had enough 
space with 146 Gigs RAID 10 and i wanted absolute throughput for our 50 
e-mail users which use Outlook with Communigate MAPI Plugin.  Sometimes 
they click on a big public sub-directory and sync between Outlook and 
the server takes place (local caching).  The user are very satisfied and 
CentOS 5 is rock solid, providing a very good service since 2 months. 
The previous server run for about 3 years without any problem, providing 
excellent service even if it was running on modest hardware: Athlon XP 
2500, Asus A7V600, 1 Gig RAM.

On another little project (friend's media file server), i assembled a 
cheap server with Asus M2N-e, Athlon Dual Core 4600+, 1 Gig DDR2 667 RAM 
, 40 Gigs IDE system drive and 4 x Western-Digital 500 Gigs RAID Editon 
(7200 RPM) data array.  I used CentOS 5 x86_64 software RAID 5 (4 x 500 
Gigs) and managed to get 35-40 MiB/s write throughput, which was much 
more than what he got using Intel ICH-8 RAID 5 on his Windoze PC (same 
drives).  The Athlon DC 4600 handles the XOR very easily (low cpu usage) 
and the bottleneck seems to be on the bus (Regular PCI  bus, 132 MiB/s 
max combined).  He's absolutely satisfied with his new CentOS 5 Samba 
server.  Combine that with WebMIN and a couple of scripts, he's stunned 
by how it's easy to use his server!  I still wonder how people are 
paying for Winblows Home server...

Hope this helped a bit!

Guy Boisvert, ing.
IngTegration inc.