On Tue, Jan 31, 2006 at 12:47:10PM -0800, Luke Lonergan wrote: >> Linux does balanced reads on software >> mirrors. I'm not sure why you think this can't improve bandwidth. It >> does improve streaming bandwidth as long as the platter STR is more than >> the bus STR. > ... Prove it. FWIW, this is on Ultra160 disks (Seagate 10000rpm) on a dual Opteron running Linux 2.6.14.3: cassarossa:~# grep md1 /proc/mdstat md1 : active raid1 sdf6[1] sda6[0] cassarossa:~# dd if=/dev/sda6 of=/dev/null bs=8k count=400000 [system at about 35% wait for I/O and 15% system, according to top] 400000+0 records in 400000+0 records out 3276800000 bytes transferred in 54,488154 seconds (60137842 bytes/sec) [system at about 45% wait for I/O and 7% system -- whoa?] 400000+0 records in 400000+0 records out 3276800000 bytes transferred in 52,523771 seconds (62386990 bytes/sec) I'm not sure if it _refutes_ the assertion that the Linux RAID-1 driver can do balancing of sequential reads, but it certainly doesn't present very much evidence in that direction. BTW, sda and sdf are on different channels of a dual-channel (onboard, connected via PCI-X) Adaptec board, so I doubt the bus is the limiting factor. /* Steinar */ -- Homepage: http://www.sesse.net/
