I have been trying to figure out why tar run by amanda was so much slower than my manual tar runs. The culprit is tar --sparse (which is on by default in amgtar) which for me maxes out 1 CPU core and reduces tar's read speed to around 130MB/s for me on a ZFS filesystem with 1GB files. I turned that option off and now it can read at 500MB/s with only 30% CPU usage.
I suspect this will also resolve the slow read speeds i have with lots of tiny files as tar was also capped on CPU there but i had assumed it was blocking on IO. -- Anton "exuvo" Olsson [email protected]
