I created a encrypted volume on top of software raid1. These are my steps:

1. Create logical partition on sda
2. Create logical partition on sdb (same size)
3. Change type to partition to 'fd' for both partitions
4. Check that the both partitions are same size and type
fdisk -l /dev/sda && fdisk -l /dev/sdb
5. partprobe
6. Make sure there are no remains from previous RAID installations on /dev/sdb by running:
mdadm --zero-superblock /dev/sda6
mdadm --zero-superblock /dev/sdb6
7. mdadm --create /dev/md4 --level=1 --raid-disks=2 /dev/sda6 /dev/sdb6
8. watch cat /proc/mdstat

9. update mdadm.conf
mdadm --examine --scan | grep mdx >> /etc/mdadm.conf

10. Load twofish module
[root@localhost ~]# modprobe twofish

11. # cryptsetup -y -c twofish-cbc-essiv:sha256 create ftdata /dev/md4
Enter passphrase:
Verify passphrase:

12. mkfs.ext3 -b 4096 -R stride=8 /dev/mapper/ftdata

13. mkdir /ftdata

14. Mount the encrypted volume:
mount -O noatime /dev/mapper/ftdata /ftdata

It mounts successfully this first time. When I cd /ftdata, I can see the lost+found dir

Now, I unmount the volume
cd ~
And now, if I try to setup my encrypted volume like this:
I get this error:
mount: you must specify the filesystem type

So I do:
The dmesg | tail shows this:
So why is it that I can't mount my encrypted volume after the first time? I am giving the correct password when it asks to. Any insights? Thanks for your help in advance.

Hello,

I see you removed the crypting right before you unmount the volume. I'm not an expert in that domain, but I would say that when you remove, the FAT looks like corrupted as :

Could you try any 'fsck' on the node '/dev/mapper/ftdata' ?

Keep me up to date. Thanks !

g33ky

The filesystem was unmounted first.
...

Examine the raid array with the file command:
sudo file -s /dev/dm4

Does it describe an encrpted filesystem?

Use "-o" instead of "-O".

You may find using Luks to be more convenient.

Sorry for the mistake... Didn't see correctly.. A bit tired tho... :|

Thanks for your efforts guys... I got an answer as to why it wasn't mounting from people at centos forums. I thought I would share here as well

When I create subsequent mapping between /dev/mapper/ftdata and /dev/md4, I need to mention the cipher I am using with the -c option. The -y is not needed any more. This is because the default is aes. If I had used aes as my cipher, then simple
cryptsetup create ftdata /dev/md4
would work.

Therefore, I have to do the following:
cryptsetup -c twofish-cbc-essiv:sha256 create ftdata /dev/md4
Enter passphrase:

Now, mounting like this has no problem:
mount -O noatime /dev/mapper/ftdata /ftdata
It mounts successfully. yay

Thanks for the update. I've always used aes & luks and didn't know that the encryption method wasn't supplied in the superblock.