[nSLUG] Data Recovery... ;-)
dlpotter at eastlink.ca
Wed Feb 4 11:50:29 AST 2009
It appears as if the problem was a corrupted superblock on the root file
In some respects this seems odd because the first indication of problems
was corrupted directory rendering on two data partitions which were
located on a separate physical drive.
As I noted in a previous post, syslog suggested the problem was
escalating so I took the system down to think about things.
I reviewed the documentation and discussions relating to various
utilities, dd, dd_recover, ddrecover, TestDisk, and GNU ddrescue. To be
honest, I never found enough information on dd_recover/ddrecover to make
an informed decision on those (if they actually exist as more than a
typo... they could use a wiki page.;-).
In the end I purchased a similar sized disk, formated it with
similar/identical partitions for the data 'recovery' and decided to try
GNU ddrescue. (The 'info' file for ddrescue offers good examples and
ddrescue can be run to retrieve the easily accessible data and then
rerun to try harder to retrieve blocks and infill the data missed during
earlier passes - it also can be run against separate copies of a
file-system (dvds for instance) and improve the data recovery expectation.
Given how much information was on the drive I launched ddrescue with
some trepidation... expecting the program to report errors
immediately.... it didn't! (report any errors...!!!!)
I ran ddrescue on the second partition with equally benign results!
On s-ata partitions (and with no errors) ddrescue reported processing
163GB with an average transfer rate of 64,557 kB/s and a second
partition of 250GB with an average transfer rate of 61,195 kB/s.
After I recovered from the shock over the lack of errors I ran fsck on
the data partitions with no errors except unclean unmount.
fsck on the root partition offered lots of minor complaints but on
completion, the system booted fine and mounted the data partitions with
I suspect that the original problem was caused by my resetting the
system while a boot was in progress... see next post for that tale of
horror, danger and suspense (hardware...)
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