Adding a device to an active RAID1 array

Hi,

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

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.

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

If there is a better forum for this question, please direct me there. In any case TIA for any help.

-Bill

There is now, thanks.

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

This is exactly the correct forum.

NeilBrown

### Diffstat output

 ./drivers/md/md.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff ./drivers/md/md.c~current~ ./drivers/md/md.c
@@ -3488,7 +3488,7 @@ static int update_raid_disks(mddev_t *md
 		bdev = bdget_disk(mddev->gendisk, 0);
 		if (bdev) {
 			mutex_lock(&bdev->bd_inode->i_mutex);
-			i_size_write(bdev->bd_inode, mddev->array_size << 10);
+			i_size_write(bdev->bd_inode, (loff_t)mddev->array_size << 10);
 			mutex_unlock(&bdev->bd_inode->i_mutex);
 			bdput(bdev);
 		}