Question on memory tuning

[jbdimanche]

I wasn't sure where to put this, and I searched the FAQs for this but couldn't find it. I am using Freenas 8.2.0b3 64 bit with 8 gigs of RAM with only 2 TB of data ZFS in stripe formation. Basically it is nothing more than a network storage to drop files until I store them later in a more permanent solution.

Autotune set the vfs.zfs.arc_max to 5008060544 and vm.kmem_size to 4865441894. My question is this, would there be any advantage to increasing these values? I notice from the memory graph it never uses more than the allocated memory. I do not run any plugins or other apps. Thank you for any opinions that anyone might have.

 

[survive]

Hi jbdimanche,

I suppose the first thing you need to ask is "is it fast enough?" Are you maxing out the network connection (assuming gig-e are you seeing ~100MB/s)? If so there's probably not much to be gained by tweaking anything.

Keep in mind that the 64 bit version really shouldn't need any tweaking if you have enough RAM and the people who wrote the autotune script ought to have a pretty good handle on what those numbers should be.

That said, you might actually want to disable the autotune script and remove the autotune entries from "Sysctrls" & "Tunables" and see if the system performs even better. I don't know if the autotune script is geared more toward extracting every last bit of performance out of a properly spec'ed filer or if it's meant to bring a measure of stability (at the cost of absolute performance) to systems with users who can't be bothered to read & abide by the system requirements.

-Will

 

[jbdimanche]

Thank you for a very clear and concise answer. The transfer speeds that I see are pretty good, about 100 to 110 MBps read and write, which is about Max speed at the moment due to only 1 gigabit ethernet connection. I do get some stuttering sometimes, where sometimes writing will stall for a second or two.. then resume back.

Now the stutter could be a network code, but sometimes it "felt" as if the server's cache got full and the writes couldn't keep up for one reason or the other and it was flushing the cache. Note, have no actual evidence to this effect, it was just a "feeling".

Been so happy with this box, it was so easy to set up that it worked from the get go. Heck the only problem I had with it was that Teracopy (3rd party application) seems to have problem with CIFS writes. I guess the tinkerer in me just wanted to see if raising the memory limits would have any additional benefit.

 

[cyberjock]

With the answer you gave, I wouldn't touch it. You know the motto "if it ain't broke don't fix it". Of course, the government's motto is "if it ain't broke, fix it till it is".

If you have a problem that actually warrants tweaking, then I'd think about it. Just don't tweak it "cause you can". :)