Date: Tue, 11 Feb 2020 16:55:52 +0100 From: Polytropon <freebsd@edvax.de> To: tech-lists <tech-lists@zyxst.net> Cc: freebsd-questions@freebsd.org Subject: Re: questions about swap (partition and file) Message-ID: <20200211165552.e122bf2c.freebsd@edvax.de> In-Reply-To: <20200211155009.GA9715@bastion.zyxst.net> References: <20200211155009.GA9715@bastion.zyxst.net>
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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. -- Polytropon Magdeburg, Germany Happy FreeBSD user since 4.0 Andra moi ennepe, Mousa, ...
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