On 12/15/05, Gilboa Davara <gilboada@xxxxxxxxxxxxxxxx> wrote:
On Thu, 2005-12-15 at 17:07 +0000, Chris Eborn wrote:
Does the output from the following commands seem odd to people?
[root@nucoda root]# hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 774 MB in 3.01 seconds = 257.52 MB/sec
[root@nucoda root]# mount /dev/md0 /array
[root@nucoda root]# hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 416 MB in 3.00 seconds = 138.55 MB/sec
[root@nucoda root]# umount /array
[root@nucoda root]# hdparm -t /dev/md0
/dev/md0:
Timing buffered disk reads: 776 MB in 3.01 seconds = 257.42 MB/sec
[root@nucoda root]#
Tha array is made of 10 scsi disks - each of which will read at around
60 MB/sec and all seems fine with the raid
device until the fs is mounted and it appears to halve the trasnfer
rate! There is no activity in the filesystem. At the moment this
is with FC2, though I have tried with FC3 and numerous kernels.
Tweaking around with block sizes and thing does change the speed of
the raw /dev/md0 - but the speed always drops when I mount the
filesystem. Can anybody explain this behaviour?
Maybe I am missing something obvious, but this is baffling me - and
what is worse is that it all worked until I upgraded the system. I
have tried to go back, even put a new system disk in and started from
scratch, but cannot get a decent read speed from the array.
Chris
I'm seeing the same behavior on my 4x36GB MD5 setup.
Mounted FS: ~105-110MB/s.
Unmount FS: ~125MB/s.
Can you check the read-ahead settings (blockdev --getra /dev/md0)
before /and/ after fs mount?
Gilboa
Hi There,
Well I am still suffering with this - I have installed Fedora Core 2
with kernel 2.6.14 and the raid is still going half speed.
I have spent quite a while playing with the readahead values (blockdev
--setra) on both the individual disks and the raid device (/dev/md0)
and they do not seem to change anything, even with extreme values
(like "blockdev --setra 0 /dev/sd[abcdefghi]"). Leads me to think that
readahead has been disabled elsewhere.
Chris
ps - Unfortunately this machine needs to be able to show 24 12 meg
files a second (that's because film runs at 24fps) - so come the new
year it may well have to fall into the windows empire :-(
