Date: Tue, 20 Feb 2007 19:27:54 +0200 From: "Clayton Milos" <clay@milos.co.za> To: <freebsd-stable@freebsd.org> Subject: Re: getting garbage faster using FreeBSD? Message-ID: <03ac01c75514$75b1c540$9503a8c0@claylaptop> References: <45D9FD35.6040702@vwsoft.com><20070219195143.GA42379@xor.obsecurity.org><45DA121E.1040803@vwsoft.com><20070220091238.c04cfceb.wmoran@collaborativefusion.com> <20070220165012.GB75535@xor.obsecurity.org>
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----- Original Message ----- From: "Kris Kennaway" <kris@obsecurity.org> To: "Bill Moran" <wmoran@collaborativefusion.com> Cc: "Volker" <volker@vwsoft.com>; <freebsd-stable@freebsd.org>; "Kris Kennaway" <kris@obsecurity.org> Sent: Tuesday, February 20, 2007 6:50 PM Subject: Re: getting garbage faster using FreeBSD? > On Tue, Feb 20, 2007 at 09:12:38AM -0500, Bill Moran wrote: >> In response to Volker <volker@vwsoft.com>: >> >> > On 02/19/07 20:51, Kris Kennaway wrote: >> > > On Mon, Feb 19, 2007 at 08:40:37PM +0100, Volker wrote: >> > >> The tape sits there since 48 hours writing a block of data every >> > >> other minute and still didn't fill up the tape completely. The >> > >> system this is running on is a P-4 3GHz machine using FreeSBIE 2.0 >> > >> (6.2-RELEASE based). >> > >> >> > >> 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. >> >> Are you actually using /dev/random and not /dev/urandom? >> >> /dev/random is "military grade" random data. It will block if it feels >> that it hasn't gathered enough entropy to satisfy your request. It will >> never provide random data at any reasonable speed, but it will provide >> high-quality random data. >> >> If you need lost of random data, use /dev/urandom, which provides data >> that _may_ be predictable under some circumstances, but will provide >> it at a decent rate of speed. > > Not true in a post 4.x world, they are symlinks and both "military > grade" with non-blocking semantics. > > Kris I do a lot of data recovery contracting. What we do for the government tax company is wipe their old tapes totally clean and unrecoverable for them. We use a device called a degausser. It creates a very strong varying magnetic field that totally wipes out everything on a tape. We've put a few hard drives on it to test it out. it TOTALLY wipes out everything on the drive include the bios sectors rendering the drive totally unusable. We can't even get it back after that. -Clay PS: Don't use it wearing a watch unless you want to lose the time.
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