So, as @rawtaz suggested, I copied the contents of repo B over to the external USB disk where repo A resides. Then I tried backing up that data:
scanned 728 directories, 11701 files in 0:00
[34:12] 100.00% 42.513 GiB / 42.513 GiB 12434 / 12434 items 0 errors ETA 0:00
duration: 34:12
snapshot abcdefgh saved
So, if for 42 gigs it takes half an hour, then for 943 GB it would take about 11 or so hours… So I huess the disk is the problem. That, or the fact that this disk is encrypted using veracrypt.
Other than that, it surprised me that backing up the same data, to the same destination, but from a different path, didn’t use the a parent snapshot (and no using parent snapshot abc... was printed. Actually, when the backup finished, it printed two separate lists of snapshots, like so:
snapshots for (host [username], paths [/original/path/mydata]):
keep 3 snapshots:
ID Date Host Tags Directory
----------------------------------------------------------------------
abcdefg 2018-02-16 15:13:55 username /original/path/mydata
oiuhjui 2018-02-17 14:11:12 username /original/path/mydata
mnjhuio 2018-02-17 14:12:44 username /original/path/mydata
----------------------------------------------------------------------
3 snapshots
snapshots for (host [username], paths [/usbdisk/mydata]):
keep 1 snapshots:
ID Date Host Tags Directory
----------------------------------------------------------------------
sdfredf 2018-01-12 19:03:02 pc /usbdisk/mydata
----------------------------------------------------------------------
1 snapshots
I wouldn’t have expected the data to be treated differently, but I guess it’s not, it’s just restic reporting it came from a different source, still doing all the deduplication work etc, right?