Re: minimum valid block size on DVD-RAM

On 07/01/2008, Martin Laabs <martin.laabs@xxxxxxxxxxxxxxxxxxxxx> 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
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