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).