Blog of Sylvain Le Gall

Yesterday, i decided to activate the so-called RAID 0 support on my P4P800 mainboard, to increase the performance of my 2 Seagate SATA disk -- bought for this purpose. The first unfortunate event was to discover that there is 3 levels of hardware RAID: controller, accelerator and fake. Of course fake RAID is not the better category and it is the one provided by my mainboard. Once, i have understood that i must use the package dmraid to activate my RAID, i fall into a syslog flood of messages concerning "attempt to access beyond end of device".

The problem is simple, the partition table are stored on the first disk of the RAID. Linux believes that he can reach the end of the device defined in the partition table of the first disk. But since, the partition table is for the whole RAID, it cannot access the last partition.

In fact, the solution is quite simple and described here . You must add files to udev and hal rules to ignore the partition found in the partition table of the first disk:

/etc/udev/rules.d/000dmraid.rules

KERNEL=="sda1", OPTIONS+="ignore_device"
KERNEL=="sda2", OPTIONS+="ignore_device"
KERNEL=="sda3", OPTIONS+="ignore_device"

(where sda1/2/3 are the partition stored on my RAID)

/etc/hal/fdi/preprobe/000dmraid.fdi

<?xml version="1.0" encoding="UTF-8"?>

<deviceinfo version="0.2">
  <device>
    <match key="scsi.model" string="ST3160811AS">
      <merge key="info.ignore" type="bool">true</merge>
    </match>
  </device>
</deviceinfo>

(where ST3160811AS is my two Seagate disks)

You should not ignore the whole disk in udev -- as i think it is suggested in the spanish web page (i don't speak spanish so i really don't know what it explains). After adding this two files, you must update your initrd:

update-initramfs -u

If you have problem with this configuration (you have ignored too much things), you can go back to the former initrd from grub command line, by editing the menu entry and editing the standard initrd to add ".bak" at the end.

At least, i got what i want:

~$ sudo hdparm -Tt /dev/mapper/isw_dhgabfaiad_RAID_Volume1

/dev/mapper/isw_dhgabfaiad_RAID_Volume1:
 Timing cached reads:   1354 MB in  2.00 seconds = 676.78 MB/sec
 Timing buffered disk reads:  426 MB in  3.01 seconds = 141.51 MB/sec

Not that bad for an old P4.