modifying a running array

modifying a running array

[Lieven Van Acker]

Hey folks,

I didn't find any direct pointers on this issue, so maybe you experts
can advice me...

I was setting up a system, had only one disk at setup time but wanted to
configure raid 1 in advance...

so I used 

mdadm --create /dev/md0 --force --run --level=1 --raid-devices=1
/dev/sda1

to create my array.

Now as I have the second disk available, after duplicating the partition
table I wanted to add add /dev/sdb1 to the array. 

But 

mdadm /dev/md0 -a /dev/sdb1 

adds this device as a spare one, so the number of active devices stays
1. I could use the build command to reinitialise the array, but I wonder
if there's a way to extend the raiddevice while it's running?

Is there any way to arrange this?

Regards,

Lieven

Re: modifying a running array

[David Greaves]

Lieven Van Acker wrote:

>Hey folks,
>
>I didn't find any direct pointers on this issue, so maybe you experts
>can advice me...
>
>I was setting up a system, had only one disk at setup time but wanted to
>configure raid 1 in advance...
>
>so I used 
>
>mdadm --create /dev/md0 --force --run --level=1 --raid-devices=1
>/dev/sda1
>  
>
On your new disk try this:
mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sdb1 missing

Then make a filesystem on it and copy over the data from /dev/md0
then stop /dev/md0

Once you've done all that try:

mdadm /dev/md1 -a /dev/sda1

I think that'll get you where you want to be.

you may want to hang back a while in case I made a typo ;)

David


PS from the manpage:
Setting a value of 1 is probably a mistake  and so requires that --force 
be specified first.
Guess what ;)

Re: modifying a running array

[Neil Brown]

On Monday November 15, lieven.vanacker@ugent.be wrote:
> Hey folks,
> 
> I didn't find any direct pointers on this issue, so maybe you experts
> can advice me...
> 
> I was setting up a system, had only one disk at setup time but wanted to
> configure raid 1 in advance...
> 
> so I used 
> 
> mdadm --create /dev/md0 --force --run --level=1 --raid-devices=1
> /dev/sda1
> 
> to create my array.
> 
> Now as I have the second disk available, after duplicating the partition
> table I wanted to add add /dev/sdb1 to the array. 
> 
> But 
> 
> mdadm /dev/md0 -a /dev/sdb1 
> 
> adds this device as a spare one, so the number of active devices stays
> 1. I could use the build command to reinitialise the array, but I wonder
> if there's a way to extend the raiddevice while it's running?


If you are running a recent 2.6 kernel and have a recent mdadm, then

  mdadm --grow /dev/md0 --raid-devices 2

will convert /dev/md0 to a 2 device raid1 array, and the spare will
start being reconstructed.

NeilBrown