[k3b] [Bug 380064] [MATSHITA BD-MLT UJ240AS] Estimated writing speed: 4046 KB/s (0,9x)*?

[Thomas Schmitt]

https://bugs.kde.org/show_bug.cgi?id=380064

--- Comment #9 from Thomas Schmitt <scdbackup at gmx.net> ---
Hi,

i see confusions about DVD and BD speed units and about SI compliant
kB = 1000 bytes versus programmer's KiB = 1024 bytes.


"Writing speed: 5678 KB/s (4,1x)" obviously implies the speed factor
for DVD of 1385 kB/s, rather than the factor of 4495 kB/s of BD.
As BD speed 5678 kB/s would be about 1.3x.
It is not clear which of both numbers is the computed one.
Combined with the growisofs message
  /dev/sr0: "Current Write Speed" is 4.1x4390KBps.
i'd expect that 5678 is wrong and should be about 18500.
(4390 KiB/s = 4495.36 kB/s.)

"Estimated writing speed: 4046 KB/s (0,9x)" on the other hand is
converted correctly.

One may ask the drive and inserted medium for its announced speed 
values by this shell command:

  dvd+rw-mediainfo /dev/sr0

A PHILIP/R04 BD-R medium in ASUS BW-16D1HT drive reports
  Write Speed #0:        8.0x4495=35968KB/s
  Write Speed #1:        6.0x4495=26976KB/s
  Write Speed #2:        4.0x4495=17984KB/s

The value "4.1x" reported by K3B could be really "4.0x" if K3B
misunderstands 17984 kB/s as 17984 KiB/s (17984*1.024/4495 = 4.0969).

One should check K3B for such 1024 = 1000 mistakes. SCSI/MMC always
reports and expects SI compliant kB/s. I.e. "k" = 1000, not 1024.
This applies to the output of dvd+rw-mediainfo and to the reply of
SCSI command GET PERFORMANCE.


If i shall guess, then "Writing speed" is what K3B asks growisofs
to use by option "-speed=4", and "Estimated writing speed" would be
the real throughput measured between K3B and growisofs.

0.9x effective speed at 4x nominal speed is not very good. Only for
a short time (around 43 %) throughput accelerated to 1.6x for a short
time.
With Defect Management enabled 4x nominal should be about 1.5x to 2x
effective throughput.

As for CDEmu, it obviously does not feel restricted to the speed wish
18.4x DVD (= 6x BD) issued by K3 to growisofs, but rather burns as fast
as the computer can copy bytes.


Have a nice day :)

Thomas

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