HP DL185 - very slow disk read speed

Hi,
I have a HP DL185 G6 Server (12 disk model) with the following spec:

• Quad Core Xeon 2.27GHz
• 6GB RAM
• HP P212 RAID controller with battery backup
• 2 x 128GB 15K SAS 3.5" (RAID-1 for the operating system)
• 4 x 750GB 7.5K SAS 3.5" (RAID-5 for the data, 2TB usable space)

The operating system is Ubuntu Server 9.10. Both drives have been formatted as EXT4.

We are finding that read speed of the RAID-5 array is poor. Disk test results below:

sudo hdparm -tT /dev/cciss/c0d1p1
/dev/cciss/c0d1p1:
Timing cached reads:      15284 MB in  2.00 seconds = 7650.18 MB/sec
Timing buffered disk reads:   74 MB in  3.02 seconds =  24.53 MB/sec

For info, the RAID-1 array performs as follows:

sudo hdparm -tT /dev/cciss/c0d0p1
/dev/cciss/c0d0p1:
Timing cached reads:      15652 MB in  2.00 seconds = 7834.26 MB/sec
Timing buffered disk reads:  492 MB in  3.01 seconds = 163.46 MB/sec

We thought this was because with no battery, read/write cache is disabled. We have bought and installed the battery backup and have used the HP bootable CD to change the cache settings to 50% read / 50% write and check cache is enabled on the drives and the controller.

Is there something I'm missing?

From serverfault fistameeny

• The RAID speed is poor but not extremely bad for such a setup. Now that you have a battery backup, you should enhance your ext4 parameters, particularly turn barriers off (they're unnecessary with a battery). Eventually you may want to try another filesystem, too (XFS is always the faster for sequential access).

  edit: When the rebuild is done, you may want to tweak some settings, particularly read-ahead and queue depth:

  blockdev  --setra 4096 /dev/sdXX
  echo 512 > /sys/block/sdXX/queue/nr_requests
  

  Try different values and see it makes any difference.

  xenny : I disagree. The RAID speed is awful. That's 1/3 of the speed of a single drive, and this is a read test, so it's not even as if there's a RAID 5 write overhead to allow for.

  fistameeny : OK, have reset all settings on the Server, upgraded the BIOS and RAID card firmware, setup the RAID arrays again, and formatted the RAID-1 as ext4 and the RAID-5 as XFS. I've added barrier=0 to the /etc/fstab for both arrays. I've set the stripe size to 256KB for the RAID-5 too. So far, the speed is roughly the same, but I guess the arrays could still be rebuilding. Will check again soon.
  From wazoox