Date: Thu, 2 Feb 2023 09:04:02 -0700 From: Alan Somers <asomers@freebsd.org> To: jbo@insane.engineer Cc: "hackers@freebsd.org" <hackers@freebsd.org> Subject: Re: Swap, ZFS & ARC Message-ID: <CAOtMX2iDupBJkPuNzpACivdxVKKKW_rHFFkaNexsSfbeCc-YBw@mail.gmail.com> In-Reply-To: <c70BKF1xrExMKWQeTJtDhOqJVqISFp9RjHFwT0XWDh3sTXyi0NMRkVhOyp_YkTXXAV7Dtm4tK4_XsOwSXuZRT39ObYtFpPoe6biv22jMNnM=@insane.engineer> References: <ysSGWaXF7vCDubzgFdov_9k6SMLNdZ3-zHV-2LOraYOxV_8yoAkDVPqDSicYsgBw1KdL6BjP4FkK1KFs7NKZ4RRXcSDxVe_Qy_i7b_5AbSI=@insane.engineer> <1689ba8c-a317-ce1f-2854-99566468a9ed@grosbein.net> <c70BKF1xrExMKWQeTJtDhOqJVqISFp9RjHFwT0XWDh3sTXyi0NMRkVhOyp_YkTXXAV7Dtm4tK4_XsOwSXuZRT39ObYtFpPoe6biv22jMNnM=@insane.engineer>
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On Thu, Feb 2, 2023 at 8:45 AM <jbo@insane.engineer> wrote:
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> ------- Original Message -------
> On Thursday, February 2nd, 2023 at 14:41, Eugene Grosbein <eugen@grosbein.net> wrote:
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> > 02.02.2023 21:28, jbo@insane.engineer wrote:
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> > > Hello folks,
> > >
> > > Based on a discussion on the forums not so long ago I tried to figure out how swap usage on a ZFS system plays together with ARC. However, I could find very little to no information on this which leads me to believe that there is some "core concept" I might be oblivious to.
> > >
> > > The main question is basically this: Your system starts to swap out data from RAM to your swap partition.
> > > This swap data on disk ultimately resides somewhere in a ZFS pool.
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> > I prefer not doing this. That is, all my systems have swap partition outside of ZFS pool.
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> This isn't really achievable on your average "single disk" desktop systems, right?
> Assuming I'm not missing something (which is why I came here to ask), a "regular" or "default" installation through the FreeBSD installer would setup a swap partition within the zpool, right?
Actually, the installer by default sets up a swap partition beside the
zroot pool. It doesn't use swap-on-zvol. Here's what it looks like:
> gpart show
=> 40 1953525088 nvd0 GPT (932G)
40 532480 1 efi (260M)
532520 1024 2 freebsd-boot (512K)
533544 984 - free - (492K)
534528 16777216 3 freebsd-swap (8.0G)
17311744 1936211968 4 freebsd-zfs (923G)
1953523712 1416 - free - (708K)
=> 40 1953525088 nvd1 GPT (932G)
40 532480 1 efi (260M)
532520 1024 2 freebsd-boot (512K)
533544 984 - free - (492K)
534528 16777216 3 freebsd-swap (8.0G)
17311744 1936211968 4 freebsd-zfs (923G)
1953523712 1416 - free - (708K)
> zpool status zroot
pool: zroot
state: ONLINE
scan: resilvered 314G in 00:10:19 with 0 errors on Sat Dec 24 22:31:04 2022
config:
NAME STATE READ WRITE CKSUM
zroot ONLINE 0 0 0
mirror-0 ONLINE 0 0 0
nvd0p4 ONLINE 0 0 0
nvd1p4 ONLINE 0 0 0
> swapinfo
Device 1K-blocks Used Avail Capacity
/dev/gpt/swap0 8388608 0 8388608 0%
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