getting garbage faster using FreeBSD?

Clayton Milos clay at
Tue Feb 20 17:28:13 UTC 2007

----- Original Message ----- 
From: "Kris Kennaway" <kris at>
To: "Bill Moran" <wmoran at>
Cc: "Volker" <volker at>; <freebsd-stable at>; "Kris 
Kennaway" <kris at>
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 at>:
>> > 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.


PS: Don't use it wearing a watch unless you want to lose the time.

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