This is what I set up for backups recently using a cheap USB-enclosure which can house 2 SATA disks and shows them as 2 USB mass-storage devices to my system (using only one USB cable). Without any further introduction, here goes the HOWTO:
First, create one big partition on each of the two disks (/dev/sdc and /dev/sdd in my case) of the exact same size. The cfdisk details are omitted here.
$ cfdisk /dev/sdc $ cfdisk /dev/sdd
Then, create a new RAID array using the mdadm utility:
$ mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdc1 /dev/sdd1
The array is named md0, consists of the two devices (--raid-devices=2) /dev/sdc1 and /dev/sdd1, and it's a RAID-1 array, i.e. data is simply mirrored on both disks so if one of them fails you don't lose data (--level=1). After this has been done the array will be synchronized so that both disks contain the same data (this process will take a long time). You can watch the current status via:
$ cat /proc/mdstat
Personalities : [raid1]
md0 : active raid1 sdd1[1] sdc1[0]
1465135869 blocks super 1.1 [2/2] [UU]
[>....................] resync = 0.0% (70016/1465135869) finish=2440.6min speed=10002K/sec
unused devices: Some more info is also available from mdadm:
$ mdadm --detail --scan
ARRAY /dev/md0 metadata=1.01 name=foobar:0 UUID=1234578:1234578:1234578:1234578
$ mdadm --detail /dev/md0
/dev/md0:
Version : 1.01
Creation Time : Sat Feb 6 23:58:51 2010
Raid Level : raid1
Array Size : 1465135869 (1397.26 GiB 1500.30 GB)
Used Dev Size : 1465135869 (1397.26 GiB 1500.30 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Sun Feb 7 00:03:21 2010
State : active, resyncing
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Rebuild Status : 0% complete
Name : foobar:0 (local to host foobar)
UUID : 1234578:1234578:1234578:1234578
Events : 1
Number Major Minor RaidDevice State
0 8 33 0 active sync /dev/sdc1
1 8 49 1 active sync /dev/sdd1
Next, you'll want to create a big partition on the RAID device (cfdisk details omitted)...
$ cfdisk /dev/md0
...and then encrypt all the (future) data on the device using dm-crypt+LUKS and cryptsetup:
$ cryptsetup --verbose --verify-passphrase luksFormat /dev/md0p1Enter your desired pasphrase here (twice) $ cryptsetup luksOpen /dev/md0p1 myraid
After opening the encrypted container with cryptsetup luksOpen you can create a filesystem on it (ext3 in my case):
$ mkfs.ext3 -j -m 0 /dev/mapper/myraid
That's about it. In future you can access the RAID data by using the steps below.
Starting the RAID and mouting the drive:
$ mdadm --assemble /dev/md0 /dev/sdc1 /dev/sdd1 $ cryptsetup luksOpen /dev/md0p1 myraid $ mount -t ext3 /dev/mapper/myraid /mnt
Shutting down the RAID:
$ umount /mnt $ cryptsetup luksClose myraid $ mdadm --stop /dev/md0
That's all. Performance is shitty due to all the data being shoved out over one USB cable (and USB itself being too slow for these amounts of data), but I don't care too much about that as this setup is meant for backups, not performance-critical stuff.
Update 04/2011: Thanks to Bohdan Zograf there's a Belorussian translation of this article now!
