>>>> 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?
>
Hm. I'd say `cdrecord ... -format` (whatever that does), if required.
Otherwise just write to it (mkfs/etc.).
Jan Engelhardt
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