>> 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.]
Jan Engelhardt
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