On Fri, 5 Oct 2007 06:25:20 -0400 (EDT), Justin Piszcz wrote:

So you have 3 SATA 1 disks:

Yeah, 3 of them in the array, there is a fourth standalone disk which
contains the root fs from which the system boots..

http://digital-domain.net/kernel/sw-raid5-issue/mdadm-D

Do you compile your own kernel or use the distribution's kernel?

Compile my own.
 

What does cat /proc/interrupts say? This is important to see if your
disk controller(s) are sharing IRQs with other devices.

$ cat /proc/interrupts 
           CPU0       CPU1       
  0:     132052  249369403   IO-APIC-edge      timer
  1:        202         52   IO-APIC-edge      i8042
  8:          0          1   IO-APIC-edge      rtc
  9:          0          0   IO-APIC-fasteoi   acpi
 14:      11483        172   IO-APIC-edge      ide0
 16:   18041195    4798850   IO-APIC-fasteoi   sata_sil24
 18:   86068930         27   IO-APIC-fasteoi   eth0
 19:   16127662    2138177   IO-APIC-fasteoi   sata_sil, ohci_hcd:usb1, ohci_hcd:usb2
NMI:          0          0 
LOC:  249368914  249368949 
ERR:          0


sata_sil24 contains the raid array, sata_sil the root fs disk

Also note with only 3 disks in a RAID-5 you will not get stellar 
performance, but regardless, it should not be 'hanging' as you have 
mentioned.  Just out of sheer curiosity have you tried the AS
scheduler? CFQ is supposed to be better for multi-user performance
but I would be highly interested if you used the AS scheduler-- would
that change the 'hanging' problem you are noticing?  I would give it
a shot, also try the deadline and noop.

I did try them briefly. I'll have another go.

You probably want to keep the nr_requessts to 128, the
stripe_cache_size to 8mb.  The stripe size of 256k is probably
optimal.

OK.

Did you also re-mount the XFS partition with the default mount
options (or just take the sunit and swidth)?

The /etc/fstab entry for the raid array is currently:

 /dev/md0                /home                   xfs
noatime,logbufs=8 1 2

and mount says

/dev/md0 on /home type xfs (rw,noatime,logbufs=8)

and /proc/mounts

/dev/md0 /home xfs rw,noatime,logbufs=8,sunit=512,swidth=1024 0 0

So I guess mount or the kernel is setting the sunit and swidth values.
 

Justin.

Andrew