WipeOut wrote: >> AFAIR asks for the data from the raid device, and the md code sends the >> request to both drives. The drive that replies with data first is the >> winner. >> So the system would be reading staggered by that method. Now writes >> are a >> different story. > > Ok, so in theory then read performance on software RAID1 may be better > than a single disk but how much better would depend on the hit rate of > the requests being distributed.. > > Whats the story on writes? > You make it sounds like there is something happening there that you > are not happy about.. writes have to be issued to both drives. assuming the drives are on seperate channels, or on a shared channel thats fast enough not to block on two current accesses, then writes should be no slower than a single drive. his description of reads is somewhat imprecise. the MD code will send the request to the drive thats least busy, not to 'both drives'. I believe it also does some elevator seek optimization (eg: if both drives are idle, it will go to the one that was last accessed closest to the new request).