Accidental FS corruption: Mapping files to blocks

[Paul Cannon <paul.cannon3128@xxxxxxxxx>]

I have accidentally damaged my XFS, and need help (and a little prayer). The way it happened will provide your daily amusement dose (and hopefully a lesson).

* What happened?

I have two file systems xfsA (18 TBs on /dev/sdc1) and xfsB (36 TBs on /dev/sdd1). They were mounted and working fine. I accidentally executed an old script that effectively ran the following command:

>ddrescue /dev/sdc /dev/sdd sdc_sdd.log

For those unfamiliar with the ddrescue command, it claims to rescue/image data from a drive A to B. It does multiple passes to rescue data with maximum efficiency.

* Why did I do it?

I am careless or dumb or may be a combination of both. But the fact that drives got remapped (sdc/sdd became sde/sdf and otherway around) might also be part of it.

* What happened to XFS on sdd (xfsB)?

Luckily, the imaging started with an offset of about 2.7 TBs. Why? Because this was a restart of ddrescue and it started from past point. IT WROTE a total of 6.1 GBs of data on sdd/xfsB

So I quickly stopped as I realized my mistake. I ran xfs_repair on xfsB. Due to the offset of 2.7 TBs, metadata seemed fine. The xfs_repair shows everything is fine. But if I extract out data using (dd skip=2.7TB) into a file -- I can see things are different! I recognize the abrupt change in a text file, exactly where the data overwritten.

* Luckily I have old copy of the original data!

So I did a rsync -rvn /olddata/ /xfsB

Nothing! No difference in any data files. I even tried mirrordir, same thing -- nothing, no difference!

* Here is what I think is going on, and I need help.

I suspect that the access time of the file/files stored at this location are perhaps in another location in inode (does this sound correct? I am a newbie to XFS). But the data itself has changed at the location.

* QUESTION: How do I find what files were stored at the location? I have an EXACT location of the range affected. Once I find the affected files, I can perhaps do further surgery.

Any help (and prayers) will be highly appreciated.

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