Re: [PATCH] md: fix device size calculation with non-persistent superblock

Neil Brown wrote:

On Monday February 23, Paul.Clements@SteelEye.com wrote:

quoted

Neil,

Currently, the device size calculation is not correct when hot-adding
devices to arrays with non-persistent superblocks. Device size is always
calculated as if there were a physical superblock on every device. The
attached simple change to hot_add_disk() fixes the problem.

Hmm.. I had always assumed that non-persistent superblocks only worked
for linear and raid0.  I'm not sure I would trust any other
configuration.

Are you seriously using raid1 with non-persistent superblocks?  

Yes, and this works fine in 2.4, as well. We opted for non-persistent
superblocks in order to support creation of raid1 mirrors over
partitions that already had filesystems or other data present (and yes,
we calculate the size of the new md device to make sure the existing
data will fit).

How do you ensure reliable re-assembly after a device failure followed by
shutdown?

There is a user-level clustering framework that sets up, monitors, and
takes down the mirror. Disk failures and other events are handled by
this framework.

--
Paul