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
