Extremely slow software RAID

[oskare100]

Hello,
First I installed CentOS 5.0 and I configured it with software RAID 1, two disks - one IDE 160 GB and one SATA 40 GB.

Here is the setup of the disks:

RAID:
~40 GB RAID 1 md0 ext3
~500 MB RAID 1 md1 swap

Disk1:
~40 gb software raid md0
~500 mb software raid md1

Disk 2:
~40 gb software raid md0
~500 mb software raid md1

After the installation I noticed that the server was very slow so I did a performace test on disk 2, here is the result:
hdparm -tT /dev/hdd first gave me:
Timing buffered disk reads: 6 MB in 3.52 seconds = 1.70 MB/sec
Timing cached reads: 488 MB in 6.92 seconds = 70.57 MB/sec

then gave me:
Timing cached reads: 392 MB in 2.01 seconds = 195.01 MB/sec
Timing buffered disk reads: 2 MB in 3.62 seconds = 566.16 kB/sec

So I assumed something was wrong with the disk and replaced it with an 80 GB IDE disk (same setup as before) and got the following results:
hdparm -tT /dev/hdd:
Timing cached reads: 4 MB in 4.69 seconds = 872.73 kB/sec
Timing buffered disk reads: 6 MB in 3.72 seconds = 1.61 MB/sec

It feels highly unlikely that there is something wrong with both of the IDE disks. So what can be the problem? Can you think of anything?

/Oskar

 

[thedaver]

It is my belief that you cannot mix physical drive types in a software RAID, certainly not in a hardware raid.

Thus, IDE and SATA - while technically from the same hardware lineage - are significantly different in performance and controls. I would not, therefore, expect such a configuration to even work. If it does work, that's a tribute to the distribution and driver authors...

I'd recommend you look for another combination to meet your needs.

D.E.R. Management - IT Project Management Consulting

http://www.dermanagement.com/

 

[oskare100]

I found the problem, the SATA ATA combined controller couldn't enable dma for the ATA drive so I added to the boot line to make bios load dma by adding it as SCSI drive. However, now I can't add the ATA CD reader. As soon as I add it the hdd stops working or the cd stops working... Any ideas?

 

[thedaver]

Pls define "stops working"... at BIOS check, mobo boot, linux hardware check, where?

D.E.R. Management - IT Project Management Consulting

http://www.dermanagement.com/

 

[oskare100]

It doesn't mount/I can't see it from the system. And if I set the CD to master I can't see the harddrive.