On Fri, Jul 08, 2011 at 09:39:26PM +0200, Piotr Durlej wrote: > Reading RAID 1 volumes can be slow because of the way reads are > interleaved: > > # dd if=/dev/rsd0c of=/dev/null bs=1m count=256 > 256+0 records in > 256+0 records out > 268435456 bytes transferred in 1.841 secs (145780529 bytes/sec) > # dd if=/dev/rsd1c of=/dev/null bs=1m count=256 > 256+0 records in > 256+0 records out > 268435456 bytes transferred in 1.774 secs (151248200 bytes/sec) > # dd if=/dev/rsd2c of=/dev/null bs=1m count=256 > 256+0 records in > 256+0 records out > 268435456 bytes transferred in 4.683 secs (57311236 bytes/sec) > # bioctl sd2 > Volume Status Size Device > softraid0 0 Online 491516657664 sd2 RAID1 > 0 Online 491516657664 0:0.0 noencl <sd1d> > 1 Online 491516657664 0:1.0 noencl <sd0d> > # ^D > > As a workaround I have produced this patch: > > http://www.durlej.net/sr1.diff
This only helps sequential reads. I think under real load this is a total wash. What if you picked the slow drive? What if you are doing heavy writes at the same time too? > > Implementing split seeks might further improve read performance, > especially as far as concurrent requests are concerned. > > Regards, > Piotr
