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 :-(
