Benefits from computing physical IDE disk geometry?
Quoted 3 lines
If RAID1 can use the generic elevator then it should. I guess it can't though.
No, but it is feeding IO requests into the elevators of the
block devices below it. For a given read, all it wants to do is pick one device to handle the work. If it could look into the queues maybe it could make better decisions.
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Chuck
Quoted 10 lines · Chuck Ebbert
Quoted 3 lines
If RAID1 can use the generic elevator then it should. I guess it can't though.
No, but it is feeding IO requests into the elevators of the
block devices below it. For a given read, all it wants to do is pick one device to handle the work. If it could look into the queues maybe it could make better decisions.
OK right. As far as I can see, the algorithm in the RAID1 code is used to select the best drive to read from? If that is the case then I don't think it could make better decisions given more knowledge. It really wants to know if the disk head is close to request x however it is impossible to tell where the disk head will be by the time request x is the next in line for that disk, regardless if it can look at the low level queues or not.
It seems to me that a better way to layer it would be to have the complex (ie deadline/AS/CFQ/etc) scheduler handling all requests into the raid block device, then having a raid scheduler distributing to the disks, and having the disks run no scheduler (fifo).
In practice the current scheme probably works OK, though I wouldn't know due to lack of resources here :P