Adding a device to an active RAID1 array

Adding a device to an active RAID1 array

[Bill Cizek]

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

Re: Adding a device to an active RAID1 array

[Neil Brown]

On Wednesday January 18, cizek@rcn.com wrote:
> 
> Hi,
> 
> Are there any known issues with changing the number of active devices in 
> a RAID1 array?

There is now, thanks.

> 
> 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?

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

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

This is exactly the correct forum.

NeilBrown

Signed-off-by: Neil Brown <neilb@suse.de>

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

diff ./drivers/md/md.c~current~ ./drivers/md/md.c
--- ./drivers/md/md.c~current~	2006-01-17 17:42:31.000000000 +1100
+++ ./drivers/md/md.c	2006-01-19 10:29:46.000000000 +1100
@@ -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);
 		}