Hello,
according to kernel code md raid0 adjusts its bdev queue max_hw_sectors
by its chunk size:
raid0.c: blk_queue_max_hw_sectors(mddev->queue, mddev->chunk_sectors);
Would it be possible to do that for other raid levels as well?
I'm specifically interested in raid1 :)
I have a raid0 over 4x dm-crypt over 4x raid1 (degraded) over 4 disks
here, and although I couldn't find the code that does that, the raid0
tuning seems to be limited to the max_hw_sectors of the underlying
queues (which makes sense, of course):
/sys/block/sdc/queue/max_hw_sectors_kb: 32767
/sys/block/sdd/queue/max_hw_sectors_kb: 32767
/sys/block/sde/queue/max_hw_sectors_kb: 32767
/sys/block/sdf/queue/max_hw_sectors_kb: 32767
/sys/block/md71/queue/max_hw_sectors_kb: 127
/sys/block/md72/queue/max_hw_sectors_kb: 127
/sys/block/md73/queue/max_hw_sectors_kb: 127
/sys/block/md74/queue/max_hw_sectors_kb: 127
/sys/block/dm-6/queue/max_hw_sectors_kb: 127
/sys/block/dm-7/queue/max_hw_sectors_kb: 127
/sys/block/dm-8/queue/max_hw_sectors_kb: 127
/sys/block/dm-9/queue/max_hw_sectors_kb: 127
/sys/block/md7/queue/max_hw_sectors_kb: 127
raid1 doesn't tune its max_hw_sectors, thus I'm stuck at 127k request
size.
As far as I can see, the tuning works well if the underling queue
supports bigger max_hw_sectors, here is a raid0 over 2x dm-crypt over
2 disks (i.e. without raid1):
/sys/block/sdg/queue/max_hw_sectors_kb: 32767
/sys/block/sdh/queue/max_hw_sectors_kb: 32767
/sys/block/dm-11/queue/max_hw_sectors_kb: 32767
/sys/block/dm-12/queue/max_hw_sectors_kb: 32767
/sys/block/md9/queue/max_hw_sectors_kb: 512
device-mapper adopts the underlying queue max_hw_sectors and raid0 tunes
itself.
Since request size is a limiting factor for dm-crypt performance, it
would be great if at least raid1 could also tune itself to the
underlying queue max_hw_sectors (or at least max_sectors).
regards
Mario
--
There is nothing more deceptive than an obvious fact.
-- Sherlock Holmes by Arthur Conan Doyle
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