I have 2 bay NAS with a single 1TB disk with by default RAID 0. The disk failed and I could not boot it up anymore. I bought a new disk, remove the 1st bay disk and insert the new one on 2nd bay and set it up and all are working with the new disk. Now set the NAS to telnet and able to enter the NAS on telnet. Inserted the 1st disk again on bay 1 and wondering how can I manually transfer the data from 1st disk to 2nd disk. Please if anyone could tell me how to do it on mdadm telnet and not by cloning I would really appreciate it. For some reason I could not mount it. I tried creating directory on mnt and mount it by mount /dev/sda /mnt/hard_drive1. and got error of:

mount: mounting /dev/sda on /mnt/hard_drive1 failed: Invalid argument

When you say NAS do you mean a common computer or is this some embedded single use nas box?

Generally you have to know what type of raid it has and then follow the raid rebuild formula.

When you swap drives some errors may appear that have nothing to do with raid. They have to do with position of the drives.

You cannot rebuild raid0 drives. If your raid originally included 2 drives in raid 0 your out of luck as your disk only contains parts of files ( possibly untrue but would require a large amount of work to recover ). If you man mdadm it should inform you how to re-add the drive back to the raid array if it was truly a raid 0 of one. You did mention however that the disk did fail so its possible its just corrupt.

Thanks for the reply exvor. I do understand that RAID 0 with two disk you most likely lost your data but mine is just single disk only. What I want to do is on my NAS box with two disk now on telnet (old and new disk) how can I transfer the data from old disk to the new disk by not doing the mirroring. You might be right that the disk might just be corrupted. So what can I do if it is corrupted? When I am trying to mount either of the two disk they could not be mounted. Could it be because they are not a clean disk?

is it really /dev/sda ? Have you tried /dev/sda1 (2,3 ..)

To be honest, I think you need to stop 'doing things' and readup on data recovery

Start with https://help.ubuntu.com/community/DataRecovery

I think RAID 0 needs two disks minimum (see here)so what you've got is, er... a disk, and a faulty one at that.

Was it partitioned, and if so, was your data on a separate patition? in which case you may be able to use the system on your new disk to mount the data partition of the old disk and get the info off that way.
If not, you'll probably not be able to mount the old disk from the new system and you've lost it.

Setting up a RAID over partitions on the same disk serves no function I can think of, no redundancy, no reduction of transfer speed. That's not how your nas set the disk up is it?

Play Bonny!