[Discuss] Recovering a corrupted usb hard drive with XFS

[abreauj at gmail.com (John Abreau)]

I have an 18TB external hard drive that recently suffered a loss. When I
first set it up, I formatted it as a single partition with an xfs
filesystem.

Yesterday I was trying to figure out how to export it via nfs, and during
one of my attempts I used "mount --bind" to mount it under /export.

Later, when I was backing out my tests, I found I was unable to unmount the
drive because it was apparently still in use by a bash process that no
longer existed. I clicked the "unmount anyway" button, and afterward
discovered that the partition was missing from the drive. /dev/sdf exists,
but /dev/sdf1 does not.

When I ran fdisk to examine the drive, it gave the following error:

Welcome to fdisk (util-linux 2.39.4).
> Changes will remain in memory only, until you decide to write them.
> Be careful before using the write command.



> The device contains 'xfs' signature and it will be removed by a write
> command. See fdisk(8) man page and --wipe option for more details.



> Device does not contain a recognized partition table.
> The size of this disk is 16.4 TiB (18000174383104 bytes). DOS partition
> table format cannot be used on drives for volumes larger than 2199023255040
> bytes for 512-byte sectors. Use GUID partition table format (GPT).


Created a new DOS (MBR) disklabel with disk identifier 0xb9e277e5.


I immediately exited fdisk without writing it out.

I tried running "xfs_repair -L /dev/sdf", which appears to
have successfully repaired the xfs filesystem, but the partition table
still has no partitions showing, and the disk still won't mount.

"xfs_info /dev/sdf" shows the following:

meta-data=/dev/sdf               isize=512    agcount=17, agsize=268435455
blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1    bigtime=0 inobtcount=0
nrext64=0
data     =                       bsize=4096   blocks=4394573824, imaxpct=5
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=521728, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

As far as I can tell, the filesystem itself is in good shape, and I just
need to fix the partition table. But I don't know how to do that without
risk of destroying the filesystem. I've had no luck googling a useful
answer.

How do I fix this?



-- 
John Abreau / Executive Director, Boston Linux & Unix
Email: abreauj at gmail.com / WWW http://www.abreau.net / PGP-Key-ID 0x920063C6
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