Re: DVD-RAM slowness and questions

zentara_at_highstream.net
Date: 01/30/05 

Date: Sun, 30 Jan 2005 09:59:05 -0500

On Sat, 29 Jan 2005 17:46:18 -0800, Chris Carlen
<crobc@BOGUSFIELD.sbcglobal.net> wrote:

>zentara@highstream.net wrote:
>> On Fri, 28 Jan 2005 09:14:53 -0800, Chris Carlen
>> <crcarle@BOGUS.sandia.gov> wrote:
>>
>>
>>>I am experimenting with a 3x DVD-RAM cartridge in a Panasonic SW-9573C
>>>drive.

>>>The question is, how can I know if I am getting the *optimum* performance?
 
>> I have noticed the same thing, and found that DVD-RAM "quality" can vary
>> over the disk....i.e. "bad spots".
>>
>> If you can stay over 600Kb/s, I would say you are doing good. The best
>> I've seen is around 800Kb/sec. The specs for the disk units should tell
>> you waht the "max" is, if I recall correctly, mine is around 1200
>> Kb/sec. But there is a different rate for reading and writing. And then

>I am using a Panasonic 3x DVD-RAM cartridge. I think this is about the
>best available.
>
>I am curious what you were using? 1x, 2x, or 3x? Cartridge or not?
>Were you writing a single big file or copying folders full of files?
>
>I have found that if I pack up my stuff into a tarball, then the write
>is done consistently at about 1.2MB/s. If I copy a bunch of folders

I'm using a Toshiba WD-2002

Specs for Transfer Rates:

DVD-RAM (ver 2/1) 2,700KB/second
                                    1,350KB/second

DVD-RAM (ver 1.) 2,812 - 6,760KB/second

DVD-ROM 1,557 - 3,600KB/second (mode 1)

CD-ROM 1,775 - 4,150KB/second (mode 2)
        
It's a 2x writer , I'm fairly certain.
I'm using 9.4 Gb, Type 4, 2-sided cartridges, so it's
about 4.5 Gb per side.

I don't think it matters whether the disks are in a cartridge or not.
I can take them out of the cartridge and run them, and they sell
blanks I can buy to put in my existing cartridges.

 I think the cartidges are just for keeping them clean. Although there
may be some "hidden vibration problems" which may affect writing
at the ends of the disks. The cartridges may affect vibrations?

>From the WD-2002 manual:
############
NOTE: High-speed drives spin the disc at a high rotational speed. If a
DVD has printing on only half of the disc, or if there is a slight
imbalance in the DVD, the imbalance is greatly magnified by the high
speed, causing the drive to vibrate or produce a fan-like noise. These
effects are inherent in the high-speed technology and do not indicate a
problem with the drive.
###########

So, this indicates to me that the drives will not operate consistently
over the entire disk. I'm guessing, as you write, you are altering the
vibration pattern of the disk, and affecting the ability to write at the
max rated speed.

That leads me to believe in the importance of the media, like
"uniformity of plastic thickness" to assure proper balance at
high rotation speed. But its all just speculation on my part. :-)

I use mine mostly to write backup files created with "dar". I started
out with the hope of writing 4 gig files in one big pass. But after I
ran into the problem with the "media dropouts", I cut my dar file
size down to 700 Meg. Now if I notice the write-rate dropping below
500 Kb/sec, I cancel that file, and start again with another disk. Some
of my "cheap ebay" disks are marked like:

A-side: 200 Kb/sec
B-side: 800 Kb/sec

or
A-side: good at 800 Kb/sec only for 1rst 2 gigabytes

Now if I wanted to use these slower rated media for just
"real random access" ,for using it like a removavble hard drive,
just to store an odd file every now and then, I don't really
notice the slowness. It's just on continuous copying of large
files.

Now I've tested these disks with ext2 and reiserfs(journaling),
and vfat and got the same results. I didn't try ext3.

Happy to compare notes with you. :-) 

-- 
I'm not really a human, but I play one on earth.
http://zentara.net/japh.html

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