HDD size increase

[flybynite]

Having done some reading and research I built a little freenas box as for backup storage, media serving etc. and as a bit of an experiment. It seems to run quite well so far.

Case: Node 304
Motherboard: ASRock E3C226D2l Server Board
CPU Corei3 4130T
RAM: 16 Gb Kingston ECC CL11
PSU: Corsair RM550
HDD: 6 x WD Green 500gb RaidZ2 Freenas 9.2

As far as the disks go I had the 500Gb WD greens around after some upgrades in other machines and decided to use them to start with while I was experimenting and getting a feel for things.

I checked them and WDIDLE'd them to 300 seconds and they are running well RaidZ2 giving enough space for now, but they are older drives and wont last forever.

I intend to upgrade the disks in size, always intending to use 2Tb disks (not decided which flavour yet) which would conform exactly to the recommendation “4Gb RAM + 1Gb per Tb storage” May either resilver one at a time or start again fresh from backup depending on things at the time.

My question is: (finally you say!) would I be causing myself a problem using 3Tb drives over the 2Tb?

I am stuck with 16Gb RAM and 18Tb is over the ideal but I have seen configs similar. It is just that 3Tb drives are becoming the value sweet spot as time goes on and I was just wondering if the system would take more than 12Tb with no problems before starting to buy them? I am happy with the build and spec otherwise and don’t want to mess it up!
I have read and searched but no-one seems to have asked this particular one (waiting to be corrected). Any thoughts or opinions would be helpful (first post so be gentle!)

 

[Dennis K.]

You should be good with 3TB drives. The rule for 1GB RAM per 1TB space, if anything, refers to the usable space. So with (6-2)*3TB=12TB you're good to go.

 

[flybynite]

Thanks for that, obviously missed the "usable" bit the manual only seems to refer to storage and I wasn't sure if it was gross or net storage. now I look harder I do see references for 1Gb per 1Tb zpool.

 

[jgreco]

You should be good with 3TB drives. The rule for 1GB RAM per 1TB space, if anything, refers to the usable space. So with (6-2)*3TB=12TB you're good to go.

That's not correct; I intentionally rewrote that bit in the manual to be a bit vague. We needed users to be making sure that they were in the right ballpark, but there isn't an actual mathematical formula for a minimum value that will actually always work right. If performance isn't a consideration, it could even be argued that it is 1GB RAM per 1TB of *USED* space (still minimum 8GB) but typically people expect to use the space their NAS has. For a busy server, it should definitely be considered to be 1GB/1TB of raw space, which gives the system more elbow room, but in reality might even need to be 2GB or 3GB/1TB.


At 16GB of RAM you're going to be fine. You could do 6 x 4TB in RAIDZ2 with 16GB if you like, and for media storage it would be just fine. For a busy departmental fileserver that ought to be 32GB though. It'd be safe with 16GB even for that use but when it gets busy it may show poor performance characteristics.

 

[panz]

I did choose 32 GB even if I'm a home user: we do a lot of Plex transcoding and, you know, other family members tend to kill you if they can't access their videos at full speed ;)

 

[jgreco]

And that's the best way to maximize your investment... don't cheap out.

 

[flybynite]

Thanks for all the replies, things a bit clearer now. Unfortunately I didn't have the option to go with 32Gb as the board only has 2 slots, it was one of the compromises I accepted when I chose the board, but it fits what I need all other ways. I accepted it was never going to be a blazing freenas unit, but all the bits seem quite well balanced and it seems to do the job for now. If I find this one runs out of steam sometime in the future I can use it as the backup and have an excuse to build another one ;-)

 

[jgreco]

He's going to do well and be just fine, he's got the right attitude... ;-)