RAM vs performance

[creepwood]

It is said that one would use 1 GB RAM for each TB of storage. I have a few questions regarding this.

Is this of total drive space? in a 4 x 2TB RAIDZ where the effetive storage is less than 6 GB, is the RAM you're using based on the 8TB of total drives or the actual 5.8TB of effective space?

Also...

How much performance degradation can you expect if you more than double the space, with 4 more drives but 3TB? (configured in two mirrors)?

I have the above configuration but not the budget to expand with RAIDZ but rather with two drives at the time (mirror) but my mobo only supports 2 x 4GB RAM.

 

[cyberjock]

Is this of total drive space? in a 4 x 2TB RAIDZ where the effetive storage is less than 6 GB, is the RAM you're using based on the 8TB of total drives or the actual 5.8TB of effective space?

It's total usable space. In your configuration, 6GB on top of the 4GB for the system.

How much performance degradation can you expect if you more than double the space, with 4 more drives but 3TB? (configured in two mirrors)

It depends on so many factors there's no way to guess. If it's an office environment where you are serving up docs and spreadsheets, nobody will probably care. If you are doing video editing, databases and running virtual machines, you'll want more RAM.

Per my presentation(in my sig) RAM is the one place where you shouldn't try to skimp. You can save alot of money with cheaper procesors, and RAM is so cheap the tradeoff is still in your favor.

Additionally, if you are to skimpy on the RAM your system will actually be unreliable and not just slow.

 

[creepwood]

Ah that's bad, my mobo (integrated CPU) mATX doesn't support more than 8 GB's of RAM. :-/ It's more or less only a media server and not many users. usually just one.

Thanks for the answers, I'll have to check if I'm getting a new platform.

 

[cyberjock]

If it's just one user and you won't be too upset if performance isn't 60MB/sec+ speeds you will probably be fine. If you are watching movies and stuff, maybe viewing your picture collection you'll probably be okay. But as cheap as hardware is these days you can build a damn good machine for cheap! You'll likely be able to stream your movies fine. If you want to stream 3 movies to 3 different rooms and still copy stuff to/from the server while streaming, I wouldn't expect it to.

Remember, streaming a movie isn't even 3MB/sec. So it doesn't take much to stream a movie. Copying large files to/from your server will suffer though. ;) It's all about how much performance you want.

If you are dedicated to building a server you can always try using your old hardware. Worst case scenario you'll have to tear it apart and put in a new motherboard and CPU. The zpool will be safe and you won't even have to reinstall FreeNAS. It will just suck having to tear it apart ;)

 

[creepwood]

Thank you so much for all the input. Hardware is dirt cheap but as a student you'll try to find a sweet spot between budget vs performance. But you're input has been valuable, I'll probably go with the IBM ServeRAID M1015 SAS/SATA 8-channel first and se how the performance go. If it lacks too much I'll buy a new mobo along with more RAM. It's about 200USD in Sweden and works with 3TB+ drives.