minimum valid block size on DVD-RAM

[Kimi]

On 07/01/2008, Martin Laabs <martin.laabs at mailbox.tu-dresden.de> wrote:
> Hi,
>
> I'm investigating a problem concerning the minimum valid block
> size accepted by DVD (writing) devices when writing
> on a DVD-RAM. (Please don't mix DVD-R, DVD-RW and DVD-RAM up
> here.)
>
> My motivation for this is the handbook chapter 18.7.9 that
> describes how to format a DVD-RAM. All listed commands works
> on a blocksize of 512 byte. This does not work for me on an
> 'Optiarc DVD RW AD-7170A/1.02' device since it refuse every
> operation with a blocksize unequal to a multiple of
> 2048 bytes.
>
> The actual inherent (physical) block-/sector size on
> a DVD-RAM is, like on nearly all other DVDs and CDs,
> realy 2048 byte so the behaviour of my device makes sense
> to me. (How should it write a quarter sector?)
>
> Now Marc Fonvieille let me know that the instructions in
> the handbook has been submitted by a DVD-RAM user. This
> means that these instruction works at least at one system.
> I'd now like to know whether most of the available DVD-writers
> are capable of writing blocks smaller than 2k. If not it
> would be worth investigating an alternativ instruction set.
> (But this is not as simple as it seems because newfs seems
> to have a bug with the -S option and also bsdlabel works
> as default on 512 byte blocks)
>
> Since I don't have access to different DVD-writers I can't
> test their behaviour regarding the minimum accepted block
> size.
>
> Therefore I'd like to ask you for a little test with
> your DVD-RAM enabled DVD-writer.
>
> 1. Insert a DVD-RAM (not DVD-R or DVD-RW!)
> 2. run 'dd if=/dev/acd0 of=/dev/null bs=512 count=1' (please adjust - if
> necessary - the device name)
> 3. run 'dd if=/dev/acd0 of=/dev/null bs=2048 count=1' (please adjust - if
> necessary - the device name)
>
> Please report me whether command 3 and command 2 succeed
> and also if command 3 succeed and command 2
> fails. The first case would mean that your dvd-write is
> capable of reading blocks smaller that 2048 bytes which
> would be very surprising for me
>
> If you have an empty DVD-RAM (or an DVD-RAM with un-
> important data) I'd pleased if you could also try a
> writing test.
>
> 1. Insert a DVD-RAM (Remark: *it will be deleted*)
> 2. run 'dd if=/dev/zero of=/dev/acd0 bs=512 count=1' (please adjust - if
> necessary - the device name)
> 3. run 'dd if=/dev/zero of=/dev/acd0 bs=2048 count=1' (please adjust - if
> necessary - the device name)
>
> Please report me whether command 3 and command 2 succeed
> ans also if command 3 succeed and command 2 fails.
> The first would mean that your dvd-write is capable of writing
> blocks with 512 bytes. That would mean that the instruction set
> of the handbook works for you.
>
> My output of the reading an writing test is
> the following:
>
> Reading:
>
> # dd if=/dev/acd0 of=/dev/null bs=512 count=1
> dd: /dev/acd0: Invalid argument
> 0+0 records in
> 0+0 records out
> 0 bytes transferred in 0.000196 secs (0 bytes/sec)
> # dd if=/dev/acd0 of=/dev/null bs=2048 count=1
> 1+0 records in
> 1+0 records out
> 2048 bytes transferred in 1.886969 secs (1085 bytes/sec)
>
> Writing:
>
> # dd if=/dev/zero of=/dev/acd0 bs=512 count=1
> dd: /dev/acd0: Invalid argument
> 1+0 records in
> 0+0 records out
> 0 bytes transferred in 0.000205 secs (0 bytes/sec)
> # dd if=/dev/zero of=/dev/acd0 bs=2048 count=1
> 1+0 records in
> 1+0 records out
> 2048 bytes transferred in 0.001600 secs (1280169 bytes/sec)
>
> You see that my device accept read and writes with
> a blocksize (or a multiple of a blocksize) of 2048 bytes
> only.
>

I can not test now, but everything I had seen previously when looking
to use DVD-RAM for a live system instead of using hard drive, plus
cheaper & easier to backup/replace, points to having a block size of
2048 bytes, even Vista it is the only option and is the default. it
works for me perfectly for over a year on a firewall & file server,
only thing I changed was the default block/frag size for UFS2 to
8096/1024. Only time I hear them spin-up is when periodic runs
daily/weekly/monthly.

> Best regards,
>   Martin Laabs
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-- 
Kimi