Date: Sun, 10 Jun 2012 18:36:31 -0600 (MDT) From: Warren Block <wblock@wonkity.com> To: Robert Huff <roberthuff@rcn.com> Cc: freebsd-questions@freebsd.org, "Ronald F. Guilmette" <rfg@tristatelogic.com> Subject: Re: Making a bootable backup (hard)disk... how? Message-ID: <alpine.BSF.2.00.1206101829330.79072@wonkity.com> In-Reply-To: <20437.14520.364554.528919@jerusalem.litteratus.org> References: <alpine.BSF.2.00.1206100543280.75580@wonkity.com> <48774.1339367039@tristatelogic.com> <20437.14520.364554.528919@jerusalem.litteratus.org>
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On Sun, 10 Jun 2012, Robert Huff wrote: > > Ronald F. Guilmette writes: > >> Warren? Just a couple more quick questions. You recommend: >> >> >> dump -C16 -b64 -0uanL -h0 -f - /usr | (cd /mnt && restore -ruf -) >> >> I'm real curious about you suggestions for the -C and -b values. >> >> I have what amounts to a personal workstation. Yea, OK, it is running >> mail, web, and FTP servers also, but fundementailly, it is not that busy >> most of the time. And it's got 4GB of main installed. On average, I >> suspect that I ain't even using half of that. >> >> Given all that, why shouldn't I specify (e.g.): -C512 -b1024 ? >> >> Wouldn't that all make the dump go faster? > > There are many possible obstacles to faster dump speed; > enumerating them is left as an exercise for the reader. > As it happens, I have a set-up very similar to what you > describe ... except with 8g of memory. A few years ago I did some > testing with various cache sizes (as part of diagnosing other > problems) and ended up with C=32. > (I should probably run the tests again, given some hardware > changes since.) > That machine's level 0 runs tonight; I will try to remember to > (retain and) post the results. -C16 is a little small because it's hard to tell how much memory someone running the example will have. I usually use -C32 on machines with plenty of memory. Remember that dump forks multiple times, so it's not 32M, but N*32M. -b64 is the largest safe buffer size to use. People have experienced problems with larger amounts.
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