The du -hs /backup/pool /backup/cpool /backup/pc/* has finished. Basically I had 1 host that was taking up 6.9 TB of data with 2.8 TB in the cpool directory and most of the other hosts averaging a GB each.
The 1 host was our file server (which I happen to know has a 2 TB volume (1.3 TB currently used) that is our main fileshare.
I looked through the error log for this pc on backups with the most errors and found thousands of these:
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
Unable to read 8388608 bytes from /var/lib/BackupPC//pc/myfileserver/new//ffileshare/RStmp got=0, seekPosn=1501757440 (0,512,147872,1499463680,2422719488)
to see which backups are doing the most damage. I'll report back once that finishes.