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Date:      Tue, 11 Feb 2020 16:55:52 +0100
From:      Polytropon <>
To:        tech-lists <>
Subject:   Re: questions about swap (partition and file)
Message-ID:  <>
In-Reply-To: <>
References:  <>

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On Tue, 11 Feb 2020 15:50:09 +0000, tech-lists wrote:
> Which is it better to have - swapfile partition or swapfile?
> I have both, on a SSD. Thing is, I can write 10x faster to the
> file than I can
> to the partition. With a 512b block size, it can write at 17MB/s
> to the
> partition, and about 120-130MB/s to the swapfile, as reported by dd.

Probably a partition is better because it saves the subsystems
accessing it to deal with the filesystem layer. A swap device
does not have a filesystem, and it's not under VFS control, so
no overhead of that kind.

However, it is possible to "emulate" a swap device with a file,
and there are probably several ways to do this (for example,
virtual node: mdconfig + swapctl, also possible as "on demand"
solution where space will only be claimed when there's an
actual need for it).

> Historically, ISTR that it was recommended to have several swap
> partitions on
> the fastest disks available, and that swapfile was slower than
> a partition
> because of something like fat translation.

It was also suggested to make the swap partition = 2 x maximum
RAM of machine... :-)

> Is this still the case nowadays?
> Is there a better way of measuring swap speed than dd?

I'm not sure. It probably depends on the swapping behaviour
implied by your actual workloads.

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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