Date: Mon, 19 Feb 2007 22:55:48 +0100 From: Volker <volker@vwsoft.com> To: Kris Kennaway <kris@obsecurity.org> Cc: freebsd-stable@freebsd.org Subject: Re: getting garbage faster using FreeBSD? Message-ID: <45DA1CE4.4020202@vwsoft.com> In-Reply-To: <20070219212532.GA43496@xor.obsecurity.org> References: <45D9FD35.6040702@vwsoft.com> <20070219195143.GA42379@xor.obsecurity.org> <45DA121E.1040803@vwsoft.com> <20070219212532.GA43496@xor.obsecurity.org>
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On 02/19/07 22:25, Kris Kennaway wrote: > On Mon, Feb 19, 2007 at 10:09:50PM +0100, Volker wrote: >> On 02/19/07 20:51, Kris Kennaway wrote: >>> On Mon, Feb 19, 2007 at 08:40:37PM +0100, Volker wrote: >>>> I suspect this to be a slow /dev/random. >>> This sounds odd to me, I get 18-20MB/sec sustained read performance >>> from /dev/random on this 2GHz system, which is probably faster than >>> your tape write speed. >> Hmm, so this might be the tape drive(r)? I'll check this out as soon >> as I'm going to write to hard disk. >> >> I'm going to make some tests with /dev/random to get the real speed. > > Yes, it could be - you should do some more tests to find out where > your bottleneck really is before trying to possibly optimize the wrong > thing. > >>>> As there is medical data on all media I really need garbage >>>> (/dev/zero wouldn't be enough for data security as this might get >>>> recovered). >>> Neither would a single pass with /dev/random, but you presumably knew >>> this. >> Yes, I know... I would like to run 5 or more passes if it's not that >> slow. >> >> Do you think playing with randoms' sysctl interface might influence >> performance? Does /dev/random automatically re-seed from time to >> time or is it seeded at boot time only? > > It re-seeds continuously, see random(4) and/or the yarrow > specification. Don't frob the sysctls until you have confirmed that > /dev/random is really your problem though. Kris, ok and thanks - it has been the person in front of the computer, who has been too stupid (could it be me??). I've played a bit on that machine using /dev/random to /dev/null and used different blocksizes. The results are somewhat around 33MB/sec (with blocksizes between 1M and 8M). Now I've played with different blocksizes while dd'ing /dev/random to the hard disk and getting similar results. dd'ing to the tape drive gives best results with blocksizes around 64k. Using blocksizes with 1k gives 230KB/sec, 8k gives 1.7MB/sec. The tape drive did not stream well and I guess that (too short block sizes) has been my problem. Now it performs well. Sorry for sending my stupidity to the list. ;) Thx, Volker
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