Messages in this thread | | | Date | Tue, 28 Feb 2006 17:05:28 -0700 | From | Rob Sims <> | Subject | Re: [slightly OT] dvdrecord 0.3.1 -- and yes, dev=/dev/cdrom works ;) |
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On Tue, Feb 28, 2006 at 01:58:34PM -0500, Phillip Susi wrote: > Jan Engelhardt wrote: > >Yes. A 650 MB *CD*-RW (DVD-RW too?) formatted in packet mode only has like > >500-something megabytes to allow for the sort of seeks required. > >On DVD+RW, you get the full 4.3 GB (4.7 gB) AFAICS.
> DVD-RAM physically is formatted like a hard disk. It is broken up into > zones that hold different numbers of sectors which are individually and > randomly read/writable. CD/DVD+-RW media is organized as a single long > groove that consists of an unbroken series of large blocks composed of > small blocks with user and control data interleaved and error corrected. > It is for this reason that historically it could only be recorded from > start to finish in one pass.
While DVD-RAM has per-sector embossing of headers, the ECC size is still 16 sectors, so writing any one sector requires a read-modify-write pass.
> There are two modern techniques to allow pseudo random write access for > all forms of CD/DVD +/- RW media. These are packet mode, and mount > rainier mode. MRW mode formats the disk into 32 KB blocks made up of > 2048 byte sectors which are individually writable as far as the OS > knows, because an MRW compliant drive is required to internally handle > any required read/modify/write cycles to update the 32 KB blocks. MRW > mode also reserves some of the disk for sector sparing which the drive > firmware also handles. MRW mode is typically used on dvd+rw media. > IIRC, this format typically "wastes" about 10% of the capacity of the > medium.
DVD+RW and theoretically DVD-RW support writing of 32K chunks randomly on the disk. DVD+RW has a tight tolerance on positioning (+/-16 bits) and DVD-RW about 150 bytes. Both rely on ECC to correct those bits, though DVD+RW obviously eats less of the ECC budget. Neither format uses a special packet format. The drives themselves are supposed to do read-modify-write as required.
> The other technique is packet mode. Packet mode formats the media into > packets of sectors and each packet can be randomly rewritten. The > current default size is only 32 sectors per packet. Each packet has 7 > sectors of linking loss so around 18% of the disk space is wasted. I > recently submitted a patch to pktcdvd and have some patches to the > udftools package to support larger packet sizes. A packet size of 128 > sectors reduces the waste to only 5.2%.
Fixed packet writing is only a CD attribute.
Using 128 sector packets will likely break UDF interchangeability, and likely even some drive firmware. -- Rob [unhandled content-type:application/pgp-signature] | |