Firstly I'd like to say I'm very lazy hacker, so this may not be the cleverest upgrade ever :-)
I have 2x 1Tb WDMBWI orginally I was using one and rsyncing it to the other as a backup (one in the garage one in the house), but as the primary became full I decided to get a 2Tb drive and use it as a backup of the two single drives.
I found a 1Tb WDMBWII drive (2x 500Gb) cheap on eBay and thought I'd bung a couple of 1.5Tb WD 64Mb ecogreens in it at they were cheap, fast and cool (<£80 each delivered).
UPGRADE (more interesting)
Firstly I pulled the A drive and did a straight dd from it to one of the new drives (slower than doing it individually but much simpler);
dd if=/dev/sdc of=/dev/sdd bs=8225280
(using 2x SATA/USB2 adaptors on a Ubuntu 9.10)
Popped the drive back in and pulled the B drive
Fired it up and all was OK (but obviously degraded)
Shut down and bunged the other new drive in (note, I think that they labeled up my drives wrongly, or somebody swapped them A was sdb and B was sda)
THIS IS VAGUELY INTERESTING
Ideally I wanted a single 3Tb md4, but it wouldn't play ball, each time I created the linear array (-llinear) it came up as 750Gb, but changing to mirrored (-l1 without changing the partitions) it gave 1.5Tb, so either the kernel isn't compiled with large block devices (nothing over 2Tb) or I've missed something - Any ideas? did the blue ring boxes come over 2Tb sizes?
So, as I'm lazy I decided to create a 500Gb mirrored chunk and two 1Tb filesystems, this means that I can still back up the two WDMBWI in their own space and also have a separate mirrored chunk for something else.
# df -k Filesystem 1K-blocks Used Available Use% Mounted on rootfs 2893544 193600 2552956 8% / /dev/root 2893544 193600 2552956 8% / /dev/md3 972344 156700 766252 17% /var /dev/md4 472733704 131240 472602464 1% /shares/internal /dev/sda6 965418772 131228 965287544 1% /shares/internal/WDMYBOOK1 /dev/sdb6 965418772 131228 965287544 1% /shares/internal/WDMYBOOK2
This was kind of what I was looking for (although I'm sure it's not other peoples cup of tea), note it seems like the fdisk is a bit clunky on the WDMBWII and I couldn't set up the extended partition (so I did it on the ubuntu box).
Oddly enough the LED's were flashing outer/inner which meant that the drive was degraded, oh but they weren't, so it must have been something I did, probably with the partitioning, a closer look showed that fuel-gauge seems to have a bug so that it expects md4 to consist of sda4 (optionally sdb4), not sda5 and sdb5 - a consequence of using an extended partition, as I'm running firmware v2.00.19 fuel-gauge is a binary unlike the old v1 which is a script, so not that easy to fix, and because it's not part of the GPL'd software no source.
So I hacked the binary to look somewhere else for the status (under /var instead) then created some symbolic links to point to the actual status;
# ls -l /var/red* lrwxrwxrwx 1 root root 32 Mar 8 18:20 /var/redirect-md1mddev-sda1state -> /sys/block/md1/md/dev-sda1/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md1mddev-sdb1state -> /sys/block/md1/md/dev-sdb1/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md2mddev-sda2state -> /sys/block/md2/md/dev-sda2/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md2mddev-sdb2state -> /sys/block/md2/md/dev-sdb2/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md3mddev-sda3state -> /sys/block/md3/md/dev-sda3/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md3mddev-sdb3state -> /sys/block/md3/md/dev-sdb3/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md4mddev-sda4state -> /sys/block/md4/md/dev-sda5/state lrwxrwxrwx 1 root root 32 Mar 8 18:21 /var/redirect-md4mddev-sdb4state -> /sys/block/md4/md/dev-sdb5/state
All is shiny now, my 1Tb drives are backed up to my hybryd 500Gb mirror/2Tb unmirrored, odd but gives me exactly what I wanted and it's all functioning as it should.