internal write-intent bitmap, chunksize, superblock

Hello.

I have just created a raid6 array with 8 1tb drives, and it uses the default metadata 0.9.

I have been reading up on write intent bitmaps, and i wish to create an internal one. I read about different chunk sizes yielding different performance costs, but one thing i wonder is, how much space is reserved in the superblock for the bitmap? and what happens if i try to create a bitmap which would take more than the reserved space?

this is the --detail of the array:
/dev/md0:

        Version : 00.90

Creation Time : Fri May 22 23:38:18 2009
Raid Level : raid6
Array Size : 5860559616 (5589.07 GiB 6001.21 GB)
Used Dev Size : 976759936 (931.51 GiB 1000.20 GB)
Raid Devices : 8
Total Devices : 8
Preferred Minor : 0
Persistence : Superblock is persistent

Update Time : Sat May 23 16:33:50 2009
State : active
Active Devices : 8
Working Devices : 8
Failed Devices : 0
Spare Devices : 0

Chunk Size : 64K

UUID : 8a52684a:161d95d0:2cd51773:dd992753 (local to host
ida)
Events : 0.7

Number Major Minor RaidDevice State
0 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
2 8 33 2 active sync /dev/sdc1
3 8 49 3 active sync /dev/sdd1
4 8 65 4 active sync /dev/sde1
5 8 81 5 active sync /dev/sdf1
6 8 97 6 active sync /dev/sdg1
7 8 113 7 active sync /dev/sdh1

mvh.
Kasper Sandberg

60K.
It won't let you.

NeilBrown