On Mon, 21 May 2012 10:43:51 +0200 Sebastian Riemer <sebastian.riemer@xxxxxxxxxxxxxxxx> wrote: > Hi list, > > I'm wondering why stacking raid1 above raid0 limits the block sizes in > the blkio queue to 4 KiB both read and write. > > The max_sectors_kb is at 512. So it's not a matter of limits. > > Could someone explain, please? Or could someone pinpoint me to the > related location in the source code? > > We've thought of using this for replication via InfiniBand/SRP. 4 KiB > chunks are completely inefficient with SRP. We wanted to do this with > DRBD first, but this is also extremely inefficient, because of chunk > sizes in the blkio queue. > > I can reproduce the small 4 KiB chunks also in a file copy benchmark > with raid 01 on ram disks. This should be fixed in linux 3.4 with commit 6b740b8d79252f13bcb7e5d3c1d NeilBrown
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