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

Alex Chekholko alex at calicolabs.com
Wed Apr 25 12:39:16 EDT 2018


"Does the amount of uptime have any affect
on the amount of spacing being used?"

Yes, your cache is empty until it gets used.

On Wed, Apr 25, 2018 at 8:51 AM, Dave LeFevre via zfs-discuss <
zfs-discuss at list.zfsonlinux.org> wrote:

>
> 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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>
>
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