How to resize RAID-1 partitions (mdraid)

[Sam Varshavchik]

Roberto Ragusa writes:

> Sam Varshavchik wrote:
>> That bad news, since these are existing partitions, so presumably the
>> raid metadata is at the end.
>> 
>> The good news is that I took a look at the current parted online manual,
>> and it looks like there's some support in parted now. The current
>> version of parted seems to accept /dev/mdX as a parameter, and the
>> resize command is documented. So, I think what I need to do is:
>> 
>> 1) Use parted to shrink the filesystem on /dev/mdX
>> 
>> 2) Use mdadm --grow to reduce the size of the /dev/mdX array
>> 
>> 3) Go back to parted, and use the "move" command to reduce the size of
>> the partition on both disks. Not the "resize" command, because I already
>> resized the filesystem, right?
> 
> Your first mail did not really describe what you want. The plan
> in your last mail seems to imply a few details.
> 
> You say "resize". Is it enlarge or shrink? It seems it is "shrink".

Both. My disk is full. I need to shrink one thing, and grow something else.

> What other partitions you have on the disks?

The disk partitions are as follows:

   Device 
/dev/sda1 /boot  100 megabytes
/dev/sda2 /     20 gigabytes
/dev/sda3 swap - 6 gigs
/dev/sda4 Extended partition
/dev/sda5 /home -- remaining space, large

The layout of /dev/sdb is the same, and each partition on /dev/sda is in a 
RAID-1 array with its peer on /dev/sdb.

All partitions, except for /dev/sda4, have their types set to "Linux raid 
autodetect" in the partition table.

That small /boot is getting to be a pain, when updating Fedora. I originally 
wanted to shrink /home by 400-500 megabytes, getting some free space appear 
before it, shifting the remain partitions over, then adding the free space 
at the end of /boot.

But I just realized that I can simply shrink the swap partition by half a 
gig, or so, at its beginning, and move / up.

So, what I think I need to do is:

1) Drop the swap partition

2) Use mdadm --grow to reduce the size of /dev/md2 (RAID-1 joining /dev/sda3 
and /dev/sdb3) by about a gigabyte

3) Change the size of this partition in the partition table, make it smaller 
by about half a gig.

4) Move the partition physically so that it ends where it used to end.

Can parted do 3 & 4? It's not clear to me what parted does with swap 
partitions, whether it just refuses to touch them, or just treats them as 
an opaque blob. I think it's better to move the partition together with its 
data. Even though this is swap, there's a RAID signature in there, and it'll 
probably be easier to just move the partition, as is, rather than me having 
to figure out how to completely drop and then create a new RAID-1 partition.

5) Use mdadm --grow --size=max, to extend the size of the partition to 
whatever mdadm thinks it should be now, then mkswap-ing an empty swap 
partition on the raid device

6) Move /dev/sd[ab]2 up. Parted can obviously do it.

7) Change the size of the /dev/sd[ab]1 partitions.

8) Use mdadm --grow --size=max to grow /dev/md0 to absorb the larger size of 
the underlying partitions.

9) Use parted to grow /boot to the larger size of the /dev/md0 array.

What I don't understand is how to change the size of an existing partition 
without touching its contents. All the actual ext3 partitions are on the 
virtual /dev/mdX devices. Logically, they are not on the underlying 
partitions. parted's docs seem to suggest that parted will want to move the 
data in the partition around, when it resizes an existing partition. I 
think, if I understand its concepts correctly, that I need to do that on 
/dev/md, not on the /dev/sd partitions. However, it goes without saying that 
if I'm simply moving a partition on a disk, without changing its size, I 
need to obviously move the data in the partition, as is, accordingly.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: not available
Url : http://lists.fedoraproject.org/pipermail/users/attachments/20100529/22a0879e/attachment.bin