I am seeing a different array size with mdadm --detail and --examine,
and I don't understand why.
I have seen this on a production systems, but I created an array in a
VM for testing purposes, and I am seeing the same results.
I have a 5 device RAID10 with created like so. It has 5 members 8GB
each. Which I believe should result in an array size of ~20GB.
mdadm -v --create /dev/md0 --assume-clean \
--level=raid10 --layout=o2 --raid-devices=5 \
--chunk=64 \
/dev/sdb2 /dev/sdc2 /dev/sdd2 /dev/sde2 /dev/sdf2
mdadm --detail reports an array size of ~20GiB
root@debian:~# mdadm --detail /dev/md0
/dev/md0:
Creation Time : Fri Mar 16 16:06:09 2012
Raid Level : raid10
Array Size : 20960960 (19.99 GiB 21.46 GB)
Used Dev Size : 8384384 (8.00 GiB 8.59 GB)
mdadm --examine reports an array size of ~16GiB
root@debian:~# mdadm --examine /dev/sdb2 /dev/sdd2 /dev/sde2 /dev/sdf2
/dev/sdb2:
Avail Dev Size : 16769024 (8.00 GiB 8.59 GB)
Array Size : 33537536 (15.99 GiB 17.17 GB)
Used Dev Size : 16768768 (8.00 GiB 8.59 GB)
Most of my testing was done on a Debian squeeze system, but I manually
compiled and installed mdadm 3.2.3 and I also saw the same confusing
output from a Gentoo based livecd with a recent kernel.
The full output of the mdadm output is pasted available here.
http://paste.debian.net/160057/
The array in the VM seems to work fine, I was able to create a
filesystem and store data on it. But the output from the --examine is
confusing.
The same is true with the use Dev size `8384384 (8.00 GiB 8.59 GB)`
versus `16768768 (8.00 GiB 8.59 GB)`.
Chris Francy
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