On Wed, 27 Mar 2013 09:23:52 -0700 Jeff Johnson <jeff.johnson@xxxxxxxxxxxxxxxxx> wrote: > And yet I have this output from /proc/mdstat: > > md1 : active raid1 sdb3[1] sda3[0] > 288567164 blocks super 1.1 [2/2] [UU] > bitmap: 3/3 pages [12KB], 65536KB chunk > > It is very strange. the responsiveness on small file i/o tends to > support the notion that this mirror really has a 64MB chunk size. This > is practically an order of magnitude larger than what is prudent. The > iowait on simple things like a sync or writing out small files seems > to support what mdstat is reporting. Of course, I'd like to change > this but how to do so without breaking the RAID or risking data is not > obvious. This is the array _bitmap_ chunk size. In simple terms, it determines granularity of array resyncs on unclean shutdowns. You can change it by mdadm --grow /dev/md1 --bitmap=none mdadm --grow /dev/md1 --bitmap=internal --bitmap-chunk=131072 But the size you already have is okay, there is no need to change it, and I'd say certainly no need to lower it (this will decrease performance). -- With respect, Roman
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