Date: Fri, 13 Apr 2018 09:22:10 -0400 From: Lowell Gilbert <freebsd-questions-local@be-well.ilk.org> To: "Ronald F. Guilmette" <rfg@tristatelogic.com> Cc: freebsd-questions@freebsd.org Subject: Re: Two questions --- SSD block sizes and buffering Message-ID: <4436zzw8al.fsf@lowell-desk.lan> In-Reply-To: <36747.1523609096@segfault.tristatelogic.com> (Ronald F. Guilmette's message of "Fri, 13 Apr 2018 01:44:56 -0700") References: <36747.1523609096@segfault.tristatelogic.com>
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"Ronald F. Guilmette" <rfg@tristatelogic.com> writes: > In message <1cc45af6-bd4b-3854-4d37-8e9343786ce6@qeng-ho.org>, > Arthur Chance <freebsd@qeng-ho.org> wrote: > >>... man newfs says >> >>-f frag-size >> The fragment size of the file system in bytes. It must be a >> power of two ranging in value between blocksize/8 and blocksize. >> The default is 4096 bytes. >> >>so it's been fixed for 4k disks. > > Swell. But that may not really do much (in the way of improving performance) > if the underlying mass storage device has a "native" block size of, say, > 128 KiB. And as I noted, it is my understanding that essentially all > flash-based mass storage devices -do- have a native block size of 128 KiB, > or perhaps even larger. That's not really relevant to performance the way it is with a spinning-platter disk, because proximate writes (or, for that matter, reads) aren't particularly more efficient than random ones. The block size really only comes to play when the native block gets re-written, which is handled internally by the device controller -- and we really don't have much insight into the algorithms it uses. > So.... When installing FreeBSD onto an SSD, would one be well advised > to perform all newfs operations with an explicit "-f 131072" option? Probably not, unless the vast majority of your files are multiple megabytes in size. And the difference still won't be in read or write speed.
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