On Mon, 07 May 2012 11:41:43 +0200 Sebastian Riemer <sebastian.riemer@xxxxxxxxxxxxxxxx> wrote: > Hi list, > > I'm wondering why max_sectors_kb is set to 127 with md raid1. > This value is at 512 on normal HDDs. > > If I do a file copy on ext4 on a normal HDD then I can see with > blktrace/blkparse that 128 KiB chunks are read and 512 KiB chunks are > written. > > With md raid it looks like this: 124 KiB, 4 KiB, 124 KiB, 4 KiB, ... . > This looks very inefficient. > > So, is there a particular reason that max_sectors_kb is set to 127? > > Cheers, > Sebastian > You didn't say which kernel you are running. However md/raid1 bases all those settings on the minimum or maximum (as appropriate) of the setting of the underlying devices, using blk_stack_limits (in block/blk-settings.c). So the likely answer is that one of your HDDs has a smaller max_sectors_kb? NeilBrown
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