Can you have too much RAM?

[antivirus]

I recently got a freenas system up and running. I've been reading a lot into how ZFS works with RAM and caching and haven't found a definitive answer. Can you have too much RAM on a ZFS system? I know the recommendation is 8GB minimum with 1GB per 1TB but are there any adverse effects of having more?

Specs are:
2x Intel Xeon L5520
96GB Ram
20TB in RaidZ2 (12 TB usable)
6TB in mirrors (3tb usable)

Also, should I run autotune or is autotune only for systems with lower RAM than recommended?

 

[Ericloewe]

No, there is no such thing as "too much RAM" (except for Windows' licensing limitations). More RAM is never bad, especially in FreeNAS.

 

[cyberjock]

Make sure to check out the manual on autotune. The answer is most likely in there. You can also check out my newbie presentation for commonly asked questions about RAM.

 

[antivirus]

Did you check out the manual on autotune? Your answer is there.
Also, if you read my noobie presentation that tells you the answer to "too much RAM?"

Thanks cyberjock! So more RAM is always better and autotune will always slow the system down. Now I'm off to run some benchmarks.

 

[danb35]

Hmmm, the manual seems somewhat inconsistent regarding autotune. These two statements appear within a few paragraphs of each other:

Autotune will always slow the system down as it caps the ARC.

If you are trying to increase the performance of your FreeNAS system and suspect that the current hardware may be limiting performance, try enabling autotune.

 

[david kennedy]

I recently got a freenas system up and running. I've been reading a lot into how ZFS works with RAM and caching and haven't found a definitive answer. Can you have too much RAM on a ZFS system? I know the recommendation is 8GB minimum with 1GB per 1TB but are there any adverse effects of having more?

Specs are:
2x Intel Xeon L5520
96GB Ram
20TB in RaidZ2 (12 TB usable)
6TB in mirrors (3tb usable)

Also, should I run autotune or is autotune only for systems with lower RAM than recommended?

--

One of those DELL C1100's you see on ebay by chance?

 

[antivirus]

--

One of those DELL C1100's you see on ebay by chance?

I actually got one of the 4u supermicro 24 bay storage servers. It came with the X8DTN+ motherboard, 96GB ECC RAM, and dual xeon L5520s. All I had to do was run memtest (ran it for almost a week!), add drives, plug in my UPS, and I was good to go from the hardware perspective.

 

[cyberjock]

Hmmm, the manual seems somewhat inconsistent regarding autotune. These two statements appear within a few paragraphs of each other:

Yeah. Autotune is basically deprecated at the present time. Here's what you need to know:

On 8.0-8.2 it was necessary if you had a big system (>96GB of RAM) to prevent ZFS from trying to use up 100% of your RAM.
The "changes" made now either don't change anything as the 9.x defaults are changed or they cap your ARC(which *always* hurts performance).

In short, there's no reason to every enable it and I recommend that it never be enabled. ;)

 

[mattlach]

I had read somewhere at some point (and I can't seem to find it now) that with REALLY large amounts of RAM some users were having trouble with the system becoming unresponsive for several seconds at a time when it decided to clear all the RAM all at once, or something like that.

I wonder if that is still the case. That being said, if I recall, the people having this issue were using an excessive amount of ram (256GB?)

 

[cyberjock]

Yes, that was a problem but AFAIK that was solved loooong ago.

 

[mattlach]

Yes, that was a problem but AFAIK that was solved loooong ago.

That is good to know! Thank you.