linux-ext4 - Re: How to recover a damaged ext4 file system?

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Message-ID: <498DDB26.3080102@redhat.com>
Date:	Sat, 07 Feb 2009 13:04:06 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Christian Ohm <chr.ohm@....net>
CC:	Theodore Tso <tytso@....edu>, Andreas Dilger <adilger@....com>,
	linux-ext4@...r.kernel.org
Subject: Re: How to recover a damaged ext4 file system?

Christian Ohm wrote:
> On Tuesday,  6 January 2009 at 14:34, Theodore Tso wrote:
>> It looks like both the primary and the backup block group descriptors
>> are bad.  I'm not sure how this happened; normally nothing touches the
>> backup block superblocks at all.  Stupid question --- are you sure the
>> partition table is sane; that's always the first thing to check.
> 
> I created a new partition on the second drive, and I hope I used exactly the
> same options. The result of fdisk -l is the following:
> 
> corrupted drive:
> 
> Disk /dev/sde: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Disk identifier: 0xaaaaaaaa
> 
>    Device Boot      Start         End      Blocks   Id  System
>    /dev/sde1               1      121601   976760032   83  Linux
> 
> new partition on similar drive:
> 
> Disk /dev/sdb: 1000.2 GB, 1000204886016 bytes
> 255 heads, 63 sectors/track, 121601 cylinders
> Units = cylinders of 16065 * 512 = 8225280 bytes
> Disk identifier: 0xaaaaaaaa
> 
>    Device Boot      Start         End      Blocks   Id  System
>    /dev/sdb1               1      121601   976760001   83  Linux
> 
> The only difference is the number of blocks of the partition, I guess since the
> start and end are the same this should be equal as well.

that's counting "cylinders" - try "fdisk -u" to be able to display (or
specify) geometry in sectors, which is not a unit open to interpretation...

-Eric

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