Re: Reason for md raid1 max_sectors_kb limited to 127?

[Sebastian Riemer <sebastian.riemer@profitbricks.com>]

On 07/05/12 13:18, NeilBrown wrote:
> 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

Thanks for your answer! Kernel version is vanilla 3.2, but I've also
tested 2.6.32. There is no difference. Distribution: Debian Squeeze.

I can even reproduce this behaviour with RAM disks:

# modprobe brd rd_nr=2 rd_size=1048576
# cat /sys/block/ram0/queue/max_sectors_kb
512
# cat /sys/block/ram1/queue/max_sectors_kb
512
# mdadm -C /dev/md200 --force --assume-clean -n 2 -l raid1 -a md
/dev/ram0 /dev/ram1
# cat /sys/block/md200/queue/max_sectors_kb
127

I'll have a look at that blk_stack_limits() function.

Cheers,
Sebastian