Hi there,

Thanks for your prompt answer!

[ ... reshaping from ... ]


 > - / is in a Raid 1 array (/dev/md0) consisting of two
 >   partitions - sda1 and sdb1 (ca. 148 GB);
 > - swap in Raid 0 (/dev/md1) - sda2 and sdb2 of ca. 1 GB each
 >   giving me 2 GB in total:

 [ ... to ... ]


 > - resize the partition containing the / file system to 27 GB
 >   keeping it in RAID 1 (/dev/md0);
 > - create a new partition of 120GB to mount /home, also in RAID
 >   1 (/dev/md2);
 > - change swap from a RAID 0 to a RAID 1, resizing it to 2GB
 >   (/dev/md1).

Yep, that's essentially it.

 > Can this be done without reinstalling everything from scratch?

 You have two mirrored disks so it is trivial.

Not so trivial to me... :)

 Break the mirroring, repartition 'sdb' say into 'sdb[123]',
 'mkfs' the 'sdb[13]' partitions, 'mkswap' the 'sdb2' partition,
 copy stuff from 'sda1' to 'sdb1' and 'sdb3', reboot from 'sdb1'
 without any RAID, repartition 'sda' in the same way as 'sdb',
 then recreate new RAID mirrors ('md0' as 'sda1' and 'sdb1'
 etc.). You can do much the same from a live CD eliminating the
 obvious steps.

Let's suppose I use a live CD. It seems safer and less error prone.
Step by step, we have:
- break the mirroring: it is my perception that this would not be
necessary as the system would not be aware of any raid. The only
problem I see here is the fact that the drives are partitioned as RAID
auto detect, but I might be seeing a problem where it is not there;

- repartition the drive and create file systems: fine, will use parted
to do it in a non-destructive manner, shrink sdb1 (ext3) to 27GB,
delete sdb2 (swap), create new sdb2 (ext3) with 120GB and create sdb3
(swap) with 2GB; I will have to set them as RAID autodetect as well,
right?

- copy stuff from sda1 to sdb1 (/) and sdb2 (/home): fine; will do
something like this 'find . -depth -print0 | sudo cpio --null --sparse
-pvd /target/';

- reboot from sdb1 without any raid: how can I do that? change
something in GRUB, or merely physically disconnecting sda? in any
case, won't sdb's partitions be seen as they should belong to a RAID?

- repartition sda: fine;

- recreate the arrays: will this be non-destructive? do I have to
recreate them as degraded (starting with sdb[123]) and then add the
other partitions (sda[123])? would this be ok, or is there a better
way of doing it? 'mdadm --create --verbose /dev/md0 --level=1
--raid-devices=2  /dev/sda1 missing';

Am I going in the right direction here?
Thanks for all the help.

 Resizing is dangerous, shrinking is very dangerous, and most
 filesystems don't support shrinking anyhow.

Would that mean that it is not possible to do it?

 > Output of /proc/mdstat: [ ... ]

 Why so much pointless stuff...

Sorry about that. It's just that I was apparently unable to
distinguish what would be necessary and what was not.


Cheers,
Tiago