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From: andy@sun-fox.demos.su (Andrew A. Vasilyev)
Newsgroups: news.software.nntp,comp.unix.bsd.freebsd.misc
Subject: Re: FreeBSD 2.1.5, INN 1.4unoff4, and mmap()
Followup-To: news.software.nntp,comp.unix.bsd.freebsd.misc
Date: 15 Jul 1996 20:15:54 GMT
Organization: Demos Online Service
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Distribution: world
Message-ID: <4se8tq$sgf@news.demos.su>
References: <mandrews.837437077@bob.wittenberg.edu> <4sdk50$9cp@news.demos.su> <4sdndm$27k@brasil.moneng.mei.com>
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Xref: euryale.cc.adfa.oz.au news.software.nntp:24423 comp.unix.bsd.freebsd.misc:23658
Joe Greco (jgreco@brasil.moneng.mei.com) wrote:
> Why would you want to do this on a news server, anyways?
1. Stripping is good :)
2. Stripping is good not only for increasing the space but
for reducing load on 1 spindel, or, in other words,
increasing the performance of the whole system.
3. There is a way of writing the metadevice drivers in such
a way that performance is proportional to the number of drives
(for so called RAID level 0) - not "Tot_speed = N * Disk_speed",
but x*N, x -> 1.0 :) (ODS as an example).
4. FreeBSD metadevice (concatenated device) does not satisfy (3) -
but I hope it would.
5. That is why I use concatenated devices, and that is why I've
written to *.freebsd :)
> Use a _large_ stripe size to increase available concurrency of accesses.
??? To increase the _concurrency_ one should have the stripe size
-> 1 cyl. for large files (to W/R the file simultaneously to/from
many spindels), or ~S for small file size when writing/reading multiple
files a time.
> You don't care about how FAST you can retrieve your 1K or 2K Usenet articles
> off of the disk. You will not derive a benefit from striping from
> bandwidth. You care about how MANY you can get off your disks in as short a
> period as possible. If you have four drives, you would ideally like to be
> able to saturate the device and have each drive doing a complete article
> fetch without involving other drives.
So the stripe size should be ~2K - the mean size of USENET article
(not alt.binaries :)).
> I use a stripe size of 65536. And it really works well.
Well, I've got the best results for 64K and 128K - but I've
measured large sequential read, not little files.
_______
ANDY