John R Pierce wrote: > 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). Ok.. That all sounds logical.. Thanks for the feedback.. I figured it would do something to make use of the two copies of the data but just wanted to check.. :)