Hi,
On Sat, Sep 18, 2004 at 11:06:31AM -0500, Jonathan Hutchins wrote:
sb=n Instead of block 1, use block n as superblock.Given that sparse superblock backups are now the norm, how does one find them if one didn't think of this before the crash?
Good question. I doubt you are the first to ask it. My guess is that someone smarter/lazier than you and I has asked this question and then written a tool to answer it but I don't know what that tool is.
Looking at the man page for ext2fs I found a reference to the mke2fs command that could help:
Additional backup superblocks can be determined by using the mke2fs program using the -n option to print out where the superblocks were created. The -b option to mke2fs, which spec- ifies blocksize of the filesystem must be specified in order for the superblock locations that are printed out to be accurate.
In the man page for mke2fs I found this:
-n causes mke2fs to not actually create a filesystem, but display what it would do if it were to create a filesystem. This can be used to determine the location of the backup superblocks for a particular filesystem, so long as the mke2fs parameters that were passed when the filesystem was originally created are used again. (With the -n option added, of course!)
The command "tune2fs -l" will tell you what the blocksize is for a partition. If you have a good partition created at about the same time you could use this to make a first guess at the blocksize for the bad partition.
From here it is a lot of trial and error and luck. Kinda makes you want to go
write down a list of backup superblocks for your favorite partitions, doesn't it?