mdadm -Db switches array to write-pending?!

[Martin Wilck <mwilck@arcor.de>]

Hi Neil, hi all,

I discovered a weird behavior of mdadm -Db - it will switch a RAID array
from read-auto state to write-pending. For DDF (and possibly other
formats) this will cause metadata writes.

If I read the code correctly, the reason is that mdadm -Db will use the
GET_BITMAP_FILE ioctl, which calls md_allow_write(). I saw this on a
CentOS 6.3 kernel but comparing the code I didn't see a difference in
recent kernels.

I am wondering if this is intentional, and if no, if anything could be
done about it. It is certainly surprising behavior.

Regards
Martin