I have 2 external drives I keep in sync, using
rsync. I perform this task regularly on either of two machines, and frequently switch from one to the other for the sake of convenience. I have 4 machines running Debian 9, and use these drives on each of them.
This morning I used the following:
rsync -ahv --delete drive-x drive-y
and was surprised to have a few hundred reported failures.
rsync: readlink_stat... failed: Input/output error (5)
rsync: rsync: recv_generator: mkdir ... failed: Read-only file system (30)
In the process to find out what happened, I remounted the drives twice, rebooted, ran
--delete and basically my normal tries to fix something that has reliably worked for a long time. Even thought about installing
rsync again. Before I would do that I decided to
rsync the 2 drives on the other machine, which I run offline.
rsync worked just the way it should.
Having read the material posted here, I installed
clamav, updated the signatures, and scanned my home directory. I use this regularly on a different machine. I found 1 and only 1 PUA, and I deleted it. I always delete PUA's. I then remounted the two drives with this machine, and added different test files and folders to each drive.
rsync -ahv --delete drive_x drive_y and everything worked fine.