Followup: Adding a device to an active RAID1 array

Quoted 4 lines · On Wednesday January 18, [email protected] wrote:

Hi,

Are there any known issues with changing the number of active devices in a RAID1 array?

There is now, thanks.

Quoted 10 lines

I'm trying to add a third mirror to an existing RAID1 array of two disks.

I have /dev/md5 as a mirrored pair of two 40 GB disks. Directly on top of it is a 40 GB XFS filesystem.

When I do "mdadm --grow /dev/md5 -n 3" the count of devices changes from 2 to 3, as expected.
If the XFS filesystem is mounted, the array size changes to 3.0 GB. If it is not mounted everything works fine.

Quoted 3 lines

Is this supposed to work, is it required that the array be inactive to add a disk, or am I just doing
something stupid?

It is supposed to work, it doesn't, but it is the code doing something stupid, not you.
Try the patch below.

The patch you gave me worked, Neil, but the I ran into an odd problem where
the change is lost after a reboot.

I have raid1 devices for both superblocks 0.90.? and 1.0
If I update the superblock 1.0 device, mdadm --detail shows the update, but if I reboot it is lost.