Date: Wed, 13 Apr 2005 16:09:15 -0700 From: Brooks Davis <brooks@one-eyed-alien.net> To: =?iso-8859-1?Q?S=F8ren?= Schmidt <sos@DeepCore.dk> Cc: FreeBSD Multimedia <freebsd-multimedia@freebsd.org> Subject: Re: Followup to DVD Burning question Message-ID: <20050413230915.GA20498@odin.ac.hmc.edu> In-Reply-To: <425D0C7B.5070707@DeepCore.dk> References: <20050413115404.34207.qmail@web41203.mail.yahoo.com> <425D0C7B.5070707@DeepCore.dk>
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[-- Attachment #1 --] On Wed, Apr 13, 2005 at 02:11:39PM +0200, Søren Schmidt wrote: > Arne Wörner wrote: > >--- Søren Schmidt <sos@DeepCore.dk> wrote: > > > >>Arne Wörner wrote: > >> > >>>That's how I do backups with a DVD-RW: > >>> tar cf - ... | dd of=/dev/acd0 obs=32k conv=osync > >>> > >>>Unluckily my DVD-RW's cannot be used for UFS with my > >>>burner... I do not know why. > >> > >>DVD-RW doesn't quite cut it for UFS, you need DVD+RW media for > >>that. > >> > > > >Why? I can read and write the same block of a DVD-RW round robin. > >I mean: > > > >>dd if=a of=/dev/acd0 bs=32k count=1 oseek=10 > >>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10 > >>dd if=b of=/dev/acd0 bs=32k count=1 oseek=10 > >>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10 > >>dd if=c of=/dev/acd0 bs=32k count=1 oseek=10 > >>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10 > > > >... > >This looks just like a hard disc to me... > > I forgot the exact details, but the DVD-RW media (or rather the DVD-RW > method of accessing RW media) doesn't allow for non 32K transfers, > whereas the DVD+RW method does read-modify-write behind the scene to get > it to work seamlessly. I guess this could be worked around in the burner > firmware but that would probably offend the DVD consortium ;) One could write a GEOM that did read-modify-write to do blocksize translation. :-) -- Brooks -- Any statement of the form "X is the one, true Y" is FALSE. PGP fingerprint 655D 519C 26A7 82E7 2529 9BF0 5D8E 8BE9 F238 1AD4 [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.1 (GNU/Linux) iD8DBQFCXaaaXY6L6fI4GtQRAjVKAKCWvndHo8faaYLKBOY+WVzo0gt72wCfQBQP +glMAq7Sv8mBZ7DsAUPfThc= =YiNs -----END PGP SIGNATURE-----
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