Date: Mon, 07 Jan 2008 17:34:49 +0100 From: "Martin Laabs" <martin.laabs@mailbox.tu-dresden.de> To: freebsd-questions@freebsd.org Subject: minimum valid block size on DVD-RAM Message-ID: <op.t4ki0bfc724k7f@martin>
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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=3D/dev/acd0 of=3D/dev/null bs=3D512 count=3D1' (please adj= ust - if = necessary - the device name) 3. run 'dd if=3D/dev/acd0 of=3D/dev/null bs=3D2048 count=3D1' (please ad= just - 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=3D/dev/zero of=3D/dev/acd0 bs=3D512 count=3D1' (please adj= ust - if = necessary - the device name) 3. run 'dd if=3D/dev/zero of=3D/dev/acd0 bs=3D2048 count=3D1' (please ad= just - 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=3D/dev/acd0 of=3D/dev/null bs=3D512 count=3D1 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=3D/dev/acd0 of=3D/dev/null bs=3D2048 count=3D1 1+0 records in 1+0 records out 2048 bytes transferred in 1.886969 secs (1085 bytes/sec) Writing: # dd if=3D/dev/zero of=3D/dev/acd0 bs=3D512 count=3D1 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=3D/dev/zero of=3D/dev/acd0 bs=3D2048 count=3D1 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. Best regards, Martin Laabs
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