So a small update, i think my problems stem from using rtorrent. Apparently the way it handles file writes leads to serious fragmentation of files. There is a patch available, but i haven’t tried it out yet.
There’s no way (that i’ve found) to check file fragmentation on files on the FS, but one file on an external drive that rtorrent saved was in over 5000 pieces for a 1.3 GB file, So i can only assume the Drobo looks the same.
after talking to support, there is no way to manually force a defrag on the FS, just let it sit idle, and it will fix itself, but you’ve got no indication that it’s doing it (without sending a diagnostic file to them, or possibly hearing disk activity when you’re not doing anything) or how long it will take.
the reading of a fragmented file, will slow everything down, so even files that aren’t fragmented are slow. as soon as you stop the read the speed jumps back up.
Which also might lead to some explanation why sometimes apple sharing is slow, as it’s trying to do something with the “slow” files, so it has problems reading the .AppleDB file that it needs to read.
One workaround to this i’ve found is to copy the slow files off the drobo, delete them off the drobo, and then put them back on. after that they go at “normal” speeds of 30-40 MB/s.
Also just did a test, and copying (not moving) the file to another folder, instead of to another drive, on the drobo also worked.