Hi

By accident I turned off the power of my machine and for some reason it 
did not do a shut down, it just turned of immediately. It has a 400GB 
media disk with an ext3 partition (on top of a lvm device) full of data. 
When I booted it up, I got an error message saying:

   "attempt to read block from file system resulted in short read
    while checking ext3 journal"

I looked it up on the net and found information saying that the 
partition table had been corrupted and that it does not match my fstab 
anymore. When I do a fdisk on the lvm device and print the partition 
table its completely empty. I dont remember the partition setup anymore, 
so I dont want to just create a new partition. In ms-dos there used to 
be a backup partition table some where on the disk, which could be 
retrieved and inserted into the main partition table if it got 
corrupted. Is there such a backup partition table on a disk created by 
linux fdisk? and how do I retrieve the copy? If not does anybody have 
any other suggestion as to how to fix the problem?

regards

tom

Tom Forsmo wrote:
> Hi
> 
> By accident I turned off the power of my machine and for some reason it 
> did not do a shut down, it just turned of immediately. It has a 400GB 
> media disk with an ext3 partition (on top of a lvm device) full of data. 
> When I booted it up, I got an error message saying:
> 
>    "attempt to read block from file system resulted in short read
>     while checking ext3 journal"
> 
> I looked it up on the net and found information saying that the 
> partition table had been corrupted and that it does not match my fstab 
> anymore. When I do a fdisk on the lvm device and print the partition 
> table its completely empty. I dont remember the partition setup anymore, 
> so I dont want to just create a new partition. In ms-dos there used to 
> be a backup partition table some where on the disk, which could be 
> retrieved and inserted into the main partition table if it got 
> corrupted. Is there such a backup partition table on a disk created by 
> linux fdisk? and how do I retrieve the copy? If not does anybody have 
> any other suggestion as to how to fix the problem?
> 
> regards
> 
> tom

Try this. I have never done it.

http://tldp.org/HOWTO/Partition/recovering.html

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Tom Forsmo staggered into the Black Sun and said:
> 400GB media disk with an ext3 partition (on top of a lvm device)

You Mean "a 400G disk with a regular x86 partition table, one of those
partitions is a PV, there's a single VG composed of that PV and only
that PV", right?  You have backups... right?  If you don't, this is the
Universe telling you why you *NEED SOME*.

> "attempt to read block from file system resulted in short read
>  while checking ext3 journal"
>
> I looked it up on the net and found information saying that the
> partition table had been corrupted and that it does not match my fstab
> anymore.

Huh?  The second paragraph doesn't necessarily follow from the first.
(If I got the first error on an LV or partition that I knew was OK, the
first thing I'd try is "e2fsck -v -b 32768 /dev/whatever" to use the
first backup superblock.)

> When I do a fdisk on the lvm device

You Mean "when I do an fdisk -l on the disk where the PV resides",
right?  PVs, VGs, and LVs don't have partition tables.  You may think
I'm nitpicking here, but Details Count when you deal with this stuff,
and when you get the details wrong, it can easily bite you in the ass.

> and print the partition table, [it's] completely empty.

How bizarre.  This is when you get out your SysRescueCD, run gparted or
parted, and use its "rescue partitions" mode.  If this disk really was
just holding data under LVM, I personally would've made one huge
partition of type 0x8e covering the whole disk.  But that's just me.

> I [don't] remember the partition setup anymore

You didn't write the output of "fdisk -l" down anywhere?  It's a good
idea to do that.

> In ms-dos there used to be a backup partition table somewhere on the
> disk, which could be retrieved and inserted into the main partition
> table if it got corrupted.

Are you sure you're not thinking about a backup FAT?  I don't think
multiple copies of the partition table get written out anywhere, which
is why I mentioned parted.  "info parted" and look up its "rescue"
command.  HTH anyway,

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On 09/07/2008 02:21 AM, Tom Forsmo wrote:
> Hi
> 
> By accident I turned off the power of my machine and for some reason it
> did not do a shut down, it just turned of immediately. It has a 400GB
> media disk with an ext3 partition (on top of a lvm device) full of data.
> When I booted it up, I got an error message saying:
> 
>   "attempt to read block from file system resulted in short read
>    while checking ext3 journal"
> 
> I looked it up on the net and found information saying that the
> partition table had been corrupted and that it does not match my fstab
> anymore. When I do a fdisk on the lvm device and print the partition
> table its completely empty. I dont remember the partition setup anymore,
> so I dont want to just create a new partition. In ms-dos there used to
> be a backup partition table some where on the disk, which could be
> retrieved and inserted into the main partition table if it got
> corrupted. Is there such a backup partition table on a disk created by
> linux fdisk? and how do I retrieve the copy? If not does anybody have
> any other suggestion as to how to fix the problem?

Aye, that big a storage and no backup ...

Try running dd to duplicate an image on some tape or another drive of
same geometry or slightly bigger in size, before you mesh things more up
with testdisk.

testdisk (1)         - Scan and repair disk partitions

Hope that helps.

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Dances With Crows wrote:
> Tom Forsmo staggered into the Black Sun and said:

>> In ms-dos there used to be a backup partition table somewhere on the
>> disk, which could be retrieved and inserted into the main partition
>> table if it got corrupted.
> 
> Are you sure you're not thinking about a backup FAT?  I don't think
> multiple copies of the partition table get written out anywhere, which
> is why I mentioned parted.  "info parted" and look up its "rescue"
> command.  HTH anyway,

DOS, and the Win successors of DOS, also made copies of the boot
sector of the FAT partition but certainly not of the MBR with
the partition table.


Regards,

Kees.

-- 
Kees Theunissen.

Kees Theunissen wrote:
> DOS, and the Win successors of DOS, also made copies of the boot
> sector of the FAT partition but certainly not of the MBR with
> the partition table.

Take a look at this MS support page, it details the /MBR option in 
fdisk, and it applies to ms-dos 6.22 and up

http://support.microsoft.com/kb/69013


But in any case you might be on to something. I dont remember all the 
details of mbr, partitions and such any more, but as far as I can 
remember a disk contains one MBR, with a partition table and 
bootstrapping code and one boot sector at the beginning of each 
partition on the disk. Ref: http://en.wikipedia.org/wiki/Mbr

how things actually work in linux with lvm and how that affects my 
problem I dont quite yet know.

regards

tom

On Sat, 06 Sep 2008 19:28:55 -0400, Tom Forsmo <spam@nospam.net> wrote:

> how things actually work in linux with lvm and how that affects my
> problem I dont quite yet know.

In a disk with multiple partitions, the mbr (first sector) will have a
table with room for 4 partition entries, one of which may be extended.

If there is an extended partition (aka logical volume), there will be
an additional partition table (again with room for 4 entries), for
each one, stored just prior to that partition.

With lvm, you could either create a partition (normally type 8e), to
contain the physical volume, or you can have lvm use the entire disk,
so the physical volume starts at sector one, where the mbr is normally
stored.  Note: If you boot a windows system with a disk that is entirely
used for lvm connected, m$ will overwrite the first sector with an mbr.

As it seems that the ext3 filesystem is being found, but has an error
with the journal, I'd try mounting it as an ext2 filesystem, to see
if you can still access the data, that way.

Regards, Dave Hodgins

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On 2008-09-07, David W. Hodgins <dwhodgins@nomail.afraid.org> wrote:
> On Sat, 06 Sep 2008 19:28:55 -0400, Tom Forsmo <spam@nospam.net> wrote:
>
>> how things actually work in linux with lvm and how that affects my
>> problem I dont quite yet know.
>
> In a disk with multiple partitions, the mbr (first sector) will have a
> table with room for 4 partition entries, one of which may be extended.
>
> If there is an extended partition (aka logical volume), there will be
> an additional partition table (again with room for 4 entries), for
> each one, stored just prior to that partition.

Isn't there a significant difference betwen an extended
partition and a logical volume?  I'm using an extended
partition (and several partitions within it), but I'm not
using what I have heard called a logical volume.

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On Sun, 07 Sep 2008 00:54:36 -0400, Robert Riches <spamtrap42@verizon.net> wrote:

> Isn't there a significant difference betwen an extended
> partition and a logical volume?  I'm using an extended
> partition (and several partitions within it), but I'm not
> using what I have heard called a logical volume.

In older Microsoft documentation, the terms logical volume, and logical drive
were often used to refer to partitions inside an extended partition.

In http://windowshelp.microsoft.com/windows/en-us/help/d9a4d35e-efdf-406c-a049-0860180129a71033.mspx
the term used is logical drive.

In http://support.microsoft.com/kb/140418 the term logical volume is used to refer
to what a linux user would call a filesystem.

Now there are logical volume management physical and logical volumes, as well
as ntfs logical volumes.

When using the term "logical volume", it's important to include the context,
so as to differentiate between extended partitions, lvm, and ntfs logical volumes.

Just to clarify my warning about using an entire disk for an lvm physical volume ...
I once used pvcreate /dev/sda (not pvcreate /dev/sda1), to create a physical volume
on a usb flash drive.  Forgot to remove the device before rebooting to windows.
M$ overwrote the first sector with a partition table, without any warning, or
messages.  Never use the entire drive for a lvm physical volume if the drive
may be connected while booting any m$ system.

Regards, Dave Hodgins

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