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Re: DVD+/-R writers

>From: Andy Polyakov <appro@fy.chalmers.se>

>> > Only once fully formated (which
>> >takes 1 hour for 1x media), DVD-RW permits for random write, but with
>> >32KB granularity. Latter means that you either have to have special
>> >kernel driver which would arrange for 32KB granularity or modify file
>> >system code to do same thing. Now note that no work (at least no visible
>> >outcome so far) has been done to accomplish either of these two
>> >alternatives under Linux (or any other Unix implementation), [presumaly]
>> >because it's damn hard.
>> So DVD+RW drives do things in firmware what you need to do in the kernel
>> if you like to have 2k granularity with DVD-RW. But this is nothing a new
>> firmware could not support.

>Specifications are very explicit about I/O granularity in DVD-RW
>Restricted Overwrite mode. You seem to be willing to bend standard to
>suit you, it's not fair play. Secondly it doesn't really matter what one
>*could* *possibly* do [to stretch something to something else], does it?

Well, it seems that you make unproven assumptions on the quality of DVD+, so
I believe that it is fair to tell people that in theory it would be possible to
enhance DVD- firmware and hardware so partially formatted media may be 
adddressed ramdomly.

>> Note that the kernel also first reads a 512 byte sector from a hard disk
>> if you like to write only 64 bytes.

>Yes. But as already implied, if you want to extend this to 32KB to
>accomodate DVD-RW Restricted Overwrite, you have to modify kernel file
>system driver. The question was "why is there random access possibility
>for DVD+RW, but not for DVD-RW?" A.

If you believe that the kernel filesystem driver needs to be modified, then 
you are taling about a broken OS.

On a typical OS, the filesystem code talks to the block abstraction layer.

This layer has been the buffer case on historic implementation and is the
semgment driver layer + VM Cache in modern implementations.
What you have to do is to change this layer to know that there may be 
32 KB Blocks.....


 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
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