bitmap status question

How do I interpret:

      bitmap: 0/117 pages [0KB], 1024KB chunk

in the mdstat output

what does it mean when it's, eg: 23/117

cu:/huge# cat /proc/mdstat
Personalities : [linear] [raid0] [raid1] [raid5] [raid4] [raid6]
md0 : active raid5 sdf1[5] sde1[4] sdd1[3] sdc1[2] sdb1[1] sda1[0]
hdb1[6](S)
      1225543680 blocks level 5, 4096k chunk, algorithm 2 [6/6] [UUUUUU]
      bitmap: 0/117 pages [0KB], 1024KB chunk

David

This refers to the in-memory bitmap (basically a cache of what's in the on-disk bitmap -- it allows bitmap operations to be more efficient).

If it's 23/117 that means there are 23 of 117 pages allocated in the in-memory bitmap. The pages are allocated on demand, and get freed when they're empty (all zeroes). The in-memory bitmap uses 16 bits for each bitmap chunk to count all ongoing writes to the chunk, so it's actually up to 16 times larger than the on-disk bitmap.

--
Paul