Mounting of Linux volumes
nick at byu.edu
Thu Dec 1 08:59:01 MST 2005
On Thursday 01 December 2005 04:12 am, James Clawson wrote:
> Greetings to my fellow Linux users,
> I need to mount two HDDs for data recovery purposes. One is a disk
> which contains three valid Linux partitions, and the other was once
> part of a RAID which spanned three disks.
> The first HDD is in a computer which will boot, but for which I have
> no username or password lists. I can mount the partitions on that
> disk while running Linux from a different HDD and, as root, change
> the ownership and permissions of all of the files on that HDD, which
> would allow me to recover the data I need from the drive. The result
> of this would be that that drive would no longer be a usable Linux
> install. As that result is not desirable, I intend to duplicate all
> of those partitions using dd and then extract the data from the
> duplicate volume. Does anyone know of a better solution to this?
You shouldn't need to change the ownership and permissions to access the files
as root. You can just mount it ro and get anything off from it that you need
without affecting the installation. (Or just edit /etc/passwd and boot it.)
> I have retrieved a fair amount of data already from the second HDD by
> use of foremost. Thank you to those on the list who recommended that
> application to me earlier this year. Unfortunately, I have
> encountered a problem using that tool, as the drive was fragmented,
> and any file larger than a few blocks seems to be broken up due to
> that fragmentation. However, I believe I have repaired the surface
> of the volume sufficiently such that where I able to reassemble the
> RAID, I believe the disk, would be usable. As the other two disks of
> the RAID are not usable, that is not an option. Is there any way to
> access the raw files on that disk without the remainder of the RAID?
> Is there any way to rebuild or reorder the segments to minimize the
> impact of fragmentation on the volume?
Depends on the raid level.
raid 0, you're out of luck. You've only got 1/3rd of the data you need.
raid 1, you're in luck, you can just treat the drive as a single volume and
continue your data recovery attempts.
raid 5, you're out of luck, You've only got 1/2 of the data you need.
If it was raid 0 or raid 5, the 'fragmentation' you're seeing is from the
blocks of the files (in 'chunk' sizes specified when the md partition is
created) are distributed between the drives in the array--IOW not all of the
data was ever even on the drive.
Additionally, if this is the case, any 'repairing' that includes moving blocks
around would make reassembling the array impossible as their location is
predefined by the array--the array would now be scrambled.
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