I'm thinking about trying out transmission and everything I'm reading says you must have a cache drive. Why can't transmission download directly to the array? It said something about it would keep all the drives spinning, but I don't understand why. If the download is complete and not uploading, why would the drives spin and why would a cache be needed?

Drives would likely remain spinning because transmission would keep file locks even when not transmitting.

 

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While everything said above is correct, another major point against torrenting to the array is file fragmentation. Torrents can create a LOT of file fragmentation on your drives; whereas downloading to one and moving to another will eliminate that.

To clarify, do you all make the download directory a separate share that is "cache only" or "uses cache"?

It needs to be "cache only". Personally, I use an "app drive" mounted through the Drive Mount plugin.

another major point against torrenting to the array is file fragmentation. Torrents can create a LOT of file fragmentation on your drives;

 

I have utorrent do the full allocation of all files before the torrent starts, that way they are contiguous.

I usually archive all torrents to another drive anyway, so it works well for me.

It's still important to use a fast drive for your torrents.

 

Can transmission do the full allocation of files at torrent initialization time?

I have Transmission, sabnzbd, Plex, CrashPlan and SickBeard installed.  I created a cache only share of Applications.  I then installed all of my applications under unique directories beneath that (/mnt/cache/Applications).  That keeps mover from manipulating anything in that structure automatically.

 

For Transmission, I created /mnt/cache/Applications/Transmission/data to store all of my torrent data.  Until I get things more automated, I simply copy the completed torrents to a regular share on the array for permanent storage while leaving the stuff in /mnt/cache/Applications/Transmission/data for ongoing seeding.  Most of the time all drives are spun down except for the cache drive (which I don't expect to ever really spin down).  That's one of the nice things of unRAID of managing disk drives and their usage efficiently--keep drives spun down when not in use.

 

I hadn't thought about file locking.  Does that actually keep a drive from spinning down if an application has the file open, but is not actively reading or writing to it?

 

There is not an option in Transmission to pre-allocate a file that I know if.