Sometimes when I try to download some torrents with my raspberry pi via transmission, my raspberry pi slows down a lot. During such times I can not view the progress with transmission-remote -l as the procedure call times out. Doing anything else like removing the torrent is mostly futile.
The same happens when I am using vnc and transmission-gtk.
I have also noticed that during the problem I am unable to enter the destination folder due to lag. The destination folder is on a USB HDD with an NTFS filesystem.
Generally after a while the transmission-daemon just crashes and suddenly I can use my raspberry pi again.