[zfs-discuss] different arcstat numbers on similar machines.

Dave LeFevre dlefevre at gmail.com
Wed Apr 25 11:51:43 EDT 2018


I am getting complaints about one of my zfs on linux installations and it
is getting into
an area of it that I don't understand much, so I wonder if any of you have
and ideas of
what I check into or a setting to tweak.

I have 3 machines that have a good amount of memory (1TB for the HPs listed
below, 512GB for the
Dell) and one of them shows quite a bit less memory usage in arcstat and I
am getting performance
complaints about its slowness.

1 and 3 below are HP ProLiant DL360 Gen9 (1 TB memory), and #2 is a
PowerEdge R730xd (512 GB).

#1  (6 - Samsung_SSD_850_EVO_2TB)    Proliant DL360 1-TB
    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c
11:00:02     0     0      0     0    0     0    0     0    0   237G  265G

#2  (spinning discs)  Dell R730xd - 512 GB
    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c
11:00:10     0     0      0     0    0     0    0     0    0   242G  251G

#3  (6 - Samsung_SSD_850_EVO_1TB)  Proliant DL360 1-TB
    time  read  miss  miss%  dmis  dm%  pmis  pm%  mmis  mm%  arcsz     c
11:00:20     0     0      0     0    0     0    0     0    0   609M  503G

With #3 so similar, why is it current using so much less memory?  Only 5gb
is currently in use on the machine.  One caveat is that it was rebooted
this morning
when I made some BIOS changes to it.  Does the amount of uptime have any
affect
on the amount of spacing being used?

I don't know how the arc memory usage is determined.  What type of
settings (if any) do I have to twiddle with?  I am kind of a newbie when it
comes
to this level of using it.

None of these have Zils running and they are all using the current ZFS in
Ubuntu 16
(0.6.5.6-0ubuntu20).
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