In the midst of building a PLEX machine out off an old Dell Optiplex slim. It only has 1 HDD slot which I would use for my 3.5" 6TB NAS drive. I want to have a separate boot drive tho for windows and some other programs, but currently have no HDD/SSD slot. Should I find a laptop drive hard drive caddy and use that, or can plex run off a linux distro on a USB drive… Any other suggestions are welcome.
Yea those Optiplex systems dont make it easy (I’ve had to deal with them at my workplace).
I think you’ve got the right idea in using a small form factor USB drive with enough capacity to run an OS like this one. Personally, running an OS on a USB drive as a permanent solution gives me the willies (generally have only done that as a troubleshooting boot alternative), though that might end up working well for your use case.
If you want a more “tech support macguyver” style solution, I’ve seen people use zip ties in a clever way to create an SSD hammock. This assumes whatever motherboard in that Optiplex has the SATA ports to support more than one drive (which I’m assuming it must).
Either way, with only one HDD as your NAS drive, you run the risk of having that drive fail at some point and losing some data. It might be worth it to find a way to run multiple drives in a RAID array of your choosing to allow for any one drive failing not ruining all your hard work.
An even more Macguyver’d solution would be to find a way to rig up more than one HDD and that SSD (running your OS) in that machine. Those things are hard to work with as it is but if its all you’ve got there are ways to make it work 
Good luck man
I wouldn’t be running a Linux distro off a USB drive unless you want to replace the USB drive very frequently.
If I where you I would just use the 3.5 6TB Nas drive and install your operating software and other programs on the same drive. So I would keep all the files on the same drive but I might partition the drive into several smaller drives. I would also make sure the Dell Optiplex slim can access a hard drive that big. Right now I am running my Plex Server on the same drive as everything else, have run it the way for almost three years without any problems.