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List:       linux-kernel
Subject:    Re: [slightly OT] dvdrecord 0.3.1 -- and yes, dev=/dev/cdrom works
From:       Bill Davidsen <davidsen () tmr ! com>
Date:       2006-02-28 22:30:54
Message-ID: 4404CF1E.2010309 () tmr ! com
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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.
>>
>> 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.
>>
> I doubt that. 10% of a 4.3 GB disk are, well, roughly 430 MB, which would 
> make df show 3.9 GB as mountpoint size, not 4.3 GB. [MB and GB are powers 
> of 1024 here.]
> 
Was that DVD recorded MtR or packet?


-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me

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