Is 15% miss in arcstat fixable without adding an L2ARC?

[jahadu]

Running:
Latest Freenas
HP Proliant Microserver Gen 8 with CPU;
Intel(R) Celeron(R) CPU G1610T @ 2.30GHz
16 GB ECC
4 x 3TB Seagate NAS HDD, Raidz2
GBe network

I'm about to start over with my installation, I've misunderstood some essential stuff about permissions, users and groups and it just feels good to start over. Someone told me that changing "Permission type" from Unix to Windows on a dataset will mess up permissions, so I'll just start over.

But first I need to get back some data from the NAS. I noticed when I uploaded via FTP I got about 110mb/s, but downloading "only" gets me 80mb/sec. And when transferring via CIFS I get about 70mb/s.

So I tried arcstat while transferring back files now and see this

Code:

[root@freenas] ~# arcstat.py 2 10
    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c
19:34:06   130    64     49     0    0    64  100     0    0    11G   11G
19:34:08  4.6K   842     18    10    0   832  100    10    1    11G   11G
19:34:10  4.4K   676     15     5    0   671  100     5    0    11G   11G
19:34:12  4.4K   776     17     8    0   768  100     8    1    11G   11G
19:34:14  4.5K   774     17     6    0   768  100     6    0    11G   11G
19:34:16  4.8K   743     15     6    0   736  100     6    0    11G   11G
19:34:19  4.7K   774     16     6    0   768  100     6    0    11G   11G
19:34:21  4.2K   676     15     5    0   671  100     5    0    11G   11G
19:34:23  4.3K   776     17     8    0   768  100     8    1    11G   11G
19:34:25  4.3K   645     15     5    0   640  100     5    0    11G   11G

Is this something that could be fixed in tunables, or would I need to get more RAM or add an SSD as a L2ARC?

The CPU usage is at 10%.

Thank you!

 

[jgreco]

At 16GB, I believe the MicroServer is already RAM-full.

Adding L2ARC to a 16GB system is more likely to be detrimental than helpful. If you are already running autotune, you are probably close to an ideal configuration.

 

[jahadu]

Ah, you're right about the RAM. Just, the 15% miss, what do you think would contribute to this? Or more like, how can I find this out?

Bonusquestion: How long am I supposed to run autotune, I read it's not supposed to be turned on all the time? If I download a huge directory with big files, say 500gb at 60mb/s (samba), would that be enough or does it need more time to adjust?

 

[jgreco]

Running autotune is a one-shot thing. It merely tweaks parameters in the system for the given hardware that it sees.

15% miss is nothing. You have very little ARC. As long as your pool is not that busy, ZFS can read it from the pool and that's just dandy. Nothing to be concerned about. Think of it instead as "85% from cache!!"