I'm on a regular Ubuntu 18.04 LTS with ext4 Filesystems.
I'm using restic to backup my machines. Restic is a backup tool that support different backends (local, sftp, aws, gcs, ..) but only one backup destination at a time. So I can't tell
"here take these folders and simultaneously back them up to dest1, dest2 and dest3 while reading every file on my host just once".
I know there are tools that would in a second step sync dest1 to dest2 etc. but I don't want to go into that discussion here.
Is it clever to have restic run once and then a second time, therefore going twice over all the files in the relevant folders in serial?
Or will my common Linux file cache work better if I run two/three restics in parallel so that the same files are read by my processes at roughly the same time?
Or will that totally overload my disk io because (at least on a HDD) the read head will potentially have to jump back and forth constantly?
(How) does HDD/SSD factor into this?
I hadn't done any performance tests myself, hoping some Filesystem/File cache experts could save me that trouble :)