16 GB RAM vs 32 GB RAM

[Kuro Houou]

So my NAS has been up and running for a little while now, doing a lot of transfers and some rsync's to my QNAP for backups. I have 16GB of RAM in it right now in a RaidZ1 config (3 drives), yes I know that might be a risk, hence backups to the QNAP. I noticed that I am pretty much sitting at 13GB wired all the time, 2GB free. I get transfer speeds normally around 110 MB/Sec, maybe a few MB/sec faster writes. But I know that at 110MB/sec, thats only 880 mbps, so only about 88% of Gigabit ethernet... I know everyone says more RAM is better with ZFS, but do I really need more RAM, its only about 150 bucks for another 16GB's, not cheap but not to expensive. Will that extra ram get me about the 95% network utilization? Maybe 120MB/sec reads and writes? Or should I just leave it as since the system say's it has 2 GB of RAM free so it isn't a RAM bottleneck?

 

[marcevan]

Usually the "more RAM is better" applies those with 8GB of RAM. 16GB seems the sweet spot.

 

[Ericloewe]

FreeNAS and ZFS will use as much RAM as you throw at them.

That said, your transfer speeds are reasonable, considering there's always overhead from the various layers of protocols being used to transfer data. More RAM won't hurt, but it won't really help either.

 

[Hyperion]

Id be happy with anything over 100 MB/sec.
RAM isn’t the bottle neck.
Try a stress test on all your drives. (HD pro etc).
You be lucky to get over 150, random.

 

[joeschmuck]

As Eric mentions, each protocol has overhead which I'm certain you are not accounting for. 110MB/sec is almost maxed out for CIFS (SMB) and I doubt you would be able to do much better, but I'm assuming that is the protocol. Also you didn't specify how you tested the transfer rates. Different tests will yield different results. How much data is on your pool also effects you results.

As for your RAM question... 16GB is a lot and typically enough for all home use. You will not gain any benefit by adding more unless you are doing some serious work on your system with lots of transactions. And I'm making an assumption that this is for a home system because you do not have a RAIDZ2 or Z3 setup.

As for your RAM issue (13GB wired), go into the GUI and turn on the Tunables. This will create a few tunable values which will maximize the use of your RAM. Also know that FreeBSD (what FreeNAS is based on) doesn't relinquish RAM when it's done with it. It hangs on to it but is available for use. Sometimes it will actually release it completely but I don't see that too often.

 

[Hyperion]

Quick answer, leave it as it is.
Rejoice in your RAM.

 

[Kuro Houou]

Thanks for all the info. Yeah its for home use, hence RAIDZ1 (I back it up to my old QNAP as well) and using CIFS. I'm pretty happy with 100-110 MB/sec.. much better the my Qnap 419p+ ever did!!