Oke this thread is about the "Hardware" part of servers and server hosting.
Hard Drive or SSD ?
So this is something most of the people i talk to don't even want to go into. The response i get is "Man it is way to much overkill". This is NOT the case. It is very simple and easy to see why. A HDD is a "Hard Drive Disk" This means it is a Spinning disk with a moving reader head, so if you want data from point A and then data from point B, your HDD speed will be as fast as the Reader arm can move from point A to point B. So this is more of a "Analog" system of data storage.
But a SSD "Solid State Drive" is a solid drive. It is a Storage Drive that has NO moving parts. Like a "Digital" data storage, this means you are not limited to the speed of your Disk spinner motor and your Reader header moving to the point it needs to. Also a SSD will have multiple "Threads" it will be able to read and write data to the drive, on different locations at once. With a HDD it cant be done since you have only 1 Reader arm. This is called "IOPS" or "Input/Output Operations Per Second".
Your analogy for "analog" system of data storage is misleading, and a bit dated.
There's cache on modern HDD controllers. Huge caches. There's multiple heads on modern HDD. The disk can read multiple blocks simultaneously. HDD geometry is an abstraction in modern HDD.
I won't argue that the disk is moving, but this isn't 1987 anymore. Gb/$, can't beat a HDD.
SSD has some limitations that weren't mentioned --
wear leveling. Enterprise grade SSD is expensive for a reason.
A SSD does not itself have threads. The application that uses persistent storage may have threads, and those threads are mediated by the OS to make access to persistent storage. In an OS that has protected memory (Windows, Linux, etc..) the OS controls access to the underlying HW, and in this case memory -- that's one of it's main functions. But the issue of threads is a red-herring and has nothing to do with the performance of the actual device.
SSD is faster to access data because the seek time (the Achilles heel of HDD) is practically irrelevant. So, if you run a process that's multi-threaded it could conceivably read different blocks of data faster IF the blocks are not used by other threads. But maybe not. Depends on what each thread is trying to do (and which block each thread wants).
Google Dining Philosopher's problem.
The Minecraft game is already loaded into RAM anyway. The use of persistent storage to save player data, or update a plugin is happening at a frequency much lower than reading and writing data allocated by the server's handling of player actions.
It feels faster to have SSD, but in the grand scheme (esp if your budget is low), HDD is fine and your users will not notice. The latency of the network connection is far bigger than ANY latency in HDD/SSD debate.
I think SSD is better since I can afford it. But if I couldn't, I know HDD's are just fine. No huhu.
...Food for thought, maybe Spaghetti (if you read the Dining Philosopher's link you get the joke)