Hi,
> The /srv partition is the largest on this machine and the testdisk
> recovery image of this
> partition (~170G) is too large to fit anywhere on the hard drive.

I'm not pretty sure, but testdisk allows you to generate an iso image of
whatever you want, i seem to remember:

https://www.cgsecurity.org/wiki/TestDisk

The following (and recently released) images of gnuinos beowulf might be
of assistance in this matter:

https://www.gnuinos.org/Beowulf/

because they contain the binaries of testdisk in /opt. So, you'll be
able to run this fantastic tool in
live mode and try to recover the lost data to another external device.
Just run (as root):

/opt/testdisk-7.2-WIP/testdisk_static

Good luck :)

HTH,

Aitor.