I have a rack of four 1TB drives all partitioned identically with three primary partitions. On each drive
- the first partition is only 64MB;
- the second is a large 900GB partition and
- the last holds all the remaining space

mdadm has been used to set up
/dev/md0 - RAID1, comprised of /dev/sda1 and /dev/sdb1
/dev/md1 - RAID5, comprised of /dev/sda2, /dev/sdb2, /dev/sdc2, /dev/sdd2
/dev/md2 - RAID5, comprised of /dev/sda3, /dev/sdb3, /dev/sdc3, /dev/sdd3

OK, so it was a silly mistake to make - but I am now need to increase the size of /dev/md0. My thinking is to reduce the size of md1 so that I can grow md0.

On md1 I have two logical volumes. I've successfully reduced the size of the volume so that I can reduce the size of md1. Now I'm at the nervous stage; I can find little written on the topic of shrinking RAID5 arrays - and even if I do this I'm unsure if I can move partitions around to regain the space I so desire.

Please I wonder if any of you can offer me some advice.

I don't think so its possible to reduce the size of RAID5 as data is distributed on all partitions and one partition can not ejected from the RAID volume, but one safe solution is to backup the 64 MB partition and then add /dev/md0 to the volume group you have already created (/dev/md1) and then create a new logical volume with the remaining space in your VG.