Abstraction leakage burning test DVD+R

[freebsd-questions at phillipsjk.ca]

Hello,

After my dump/restore test failed back in May of 2010[1], I finally got 
around to burning a test DVD after installing about 2.5 inches of 
semi-rigid foam under the machine to dampen any local vibration.

In designing the test, I was under the mistaken impression that buffer 
under-runs would reduce the amount of space for writing. Apparently, 
DVD+R media supports loss-less linking[2].


Test Procedure (using ATAPI interface, rather than the newer ATAPI/CAM 
interface). The man pages do not imply any major differences for this 
test. The drive in question is a LG drive with the SuperMulti logo.

Test procedure:
1.# mkfifo auxout aux45G

2. In other terminals:
# cat auxout | md5
# dd if=aux45G count=2197266 bs=2048 | md5

3. Write test disk:
# dd if=/dev/urandom bs=2048 count=2295104 | \
 tee auxout aux45G | dd of=/dev/acd0 bs=2048

Error:
dd:/dev/acd0: Input/output error
679+0 records in
678+0 records out
1388544 bytes transferred in 80.97 seconds 
(step 4 not completed due to premature burn failure after 684 
blocks, 80 seconds (from 'dd if=aux45G'...) (15743 bytes/sec))
Drive spun up at least twice during this time.

4. Read test (in another term 'cat aux45G | md5')
# dd if=/dev/acd0 bs=2048 count=2295104 | tee aux45G | md5

Questions:
Currently, the drive is locked. Before forcefully ejecting it and 
risking an new disk, I want to know what may have gone wrong. Was 
I expecting too much of FreeBSD on old hardware? 

The hardware is a Pentium-II desktop machine with 256MB of RAM, with a 
Promise ATA100 controller card. An extra-long 80-wire cable is in use 
(to ad4).
acd0: DVDR <HL-DT-STDVD-RAM GSA-H55N/1.03> at ata-1-master UDMA33
ad4: 78167MB <Maxtor 6Y080L0 YAR41WB0> at ata-2-master UDMA100

dd if=/dev/urandom of=/home/test
Wrote at 4485315 bytes/second: faster than I was expecting (based on 
linux's slow urandom function), but still slow enough to cause buffer 
under-runs. So the second question is: do I have to do anything special 
to enable buffer underrun protection? (with DVD+R's lossless linking 
feature, no data should be lost.)

How important is running ATAPI/CAM? Obviously DVD burning was happening 
before the release of version 8, as far as I know.

If running out of data is supposed to be abstracted away, did I find a 
bug that only shows up on old hardware or heavy load? (Or possibly drive 
firmware bug?)

Regards,

James Phillips

# uname -a
FreeBSD dusty.inet 8.0-RELEASE FreeBSD 8.0-RELEASE #0: Sat Nov 21 
15:48:17 UTC 2009  
root at almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386

[1] dump/restore (to DVD+R) test failure
http://docs.freebsd.org/cgi/getmsg.cgi?fetch=290415+0+archive/2010/freebsd-questions/20100530.freebsd-questions

[2] Why DVD+R(W) is superior to DVD-R(W)
http://www.myce.com/article/Why-DVDRW-is-superior-to-DVD-RW-203/

PS: is signing messages on the mailing list a faux-pas?

-- 
OpenPGP Public Key: http://phillipsjk.ca/signature0611.txt

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