Re: raidtools to mdadm

[Bill Davidsen <davidsen@tmr.com>]

Casey Boone wrote:
> ok so i am trying to recover some data for a friend.  what i am 
> wanting to do is forcibly set up /dev/mdN to be a raid0 of /dev/sda 
> and /dev/sdb
>
> i do not want to actually change any of the contents of these drives, 
> just mount very simply as a raid0.  the raid was originally created 
> using an onboard nvidia raid on the motherboard these drives used to 
> be hooked to.  my friend thought he could shove them into another 
> windows box (that is what he was running on them) and have windows 
> recover the raid.  all this did was totally destroy the superblock on 
> one of the two drives.  dmraid now wont see them as a matched pair so 
> that is out.  the actual data areas of both drives seems to be intact, 
> but unless i can get them into raid0 i dont know how i can recover the 
> data.  it figures he gives me the drives after he makes it a notch or 
> two more of a pain :\
>
I have friends like that too. ;-)

>
> now before the advent of mdadm i would use /etc/raidtab and have no 
> issues setting up the raid device. \

I haven't used raidtools for ages, but can't you bring yourself to using 
them now? I seem to remember that there was no superblock to be written 
in a bad place, which might be an advantage. mdadm has several versions 
which write the superblock in various places on the drives, and you may 
want "none of the above."

Alternatively, if these are fairly small, write a tiny program to open 
both physical devices, read a chunk from one, then the other, repeat 
while writing to something not hosed.
>
>
> as best i can tell i am using the correct commands for what i want but 
> i pretty much get nothing but errors:
>
> root@Knoppix:/media# mdadm --build /dev/md1 --chunk=128 --level=0 
> --raid-devices=2 /dev/sda /dev/sdb
> mdadm: error opening /dev/md1: No such device or address
> root@Knoppix:/media# mdadm --build -n 2 -c 128 -l 0 /dev/md1 /dev/sda 
> /dev/sdb
> mdadm: error opening /dev/md1: No such device or address
>
>
> when i run those commands i do get /dev/mdN entries created, but they 
> do not point to a valid block device (as tested with fdisk -l and with 
> dmraid -b)
>
>
> for the life of me i dont understand why anyone would put important 
> data on a raid0, but that is what happened in this case.
>
>
> If i have to i will drop down to an older knoppix release to get 
> raidtools back, as i have never had any issues in recovering crap 
> onboard raid arrays nor windows software raid arrays under it.  i am 
> sure it can be done with mdadm but for the life of me i cannot seem to 
> figure out exactly how.
>
> any help on this would be greatly appreciated
>
> Casey 


-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979