Control of read speed on CD-ROM

Control of read speed on CD-ROM

Post by Mark Ayzenshtey » Sat, 13 Mar 1999 04:00:00

Hi all,

I have a Panasonic 7502 SCSI CDR under 2.0.33 slackware and I would like
to bring down its read speed in linux from 8X to say 4X. Is there a tool
to do this? I know there is one for plextor drives, but what about for
SCSI CD-ROM's in general?



                Mark Ayzenshteyn CS Major at UCSD      



1. CD-ROM read speed slower than expected

I did some timings of the read speed of two CD drives I have attached
to my Transmonde Vivante SE Celeron 300 laptop which runs linux
(kernel version 2.0.36).  The first drive is an internal IDE 24x
CD-ROM and the second is an external SCSI Yamaha 4416S which is
advertised as a 16x read drive and is attached through an Adaptec
1460B PCMCIA card.

To do the timing on my internal 24x drive I did:

  time dd if=/dev/cdrom of=/dev/null bs=512 count=100000

with a data CD-ROM in the drive.  To read 50M it took 37.25 seconds.
(I tried varying the block size, and 512 bytes was the fastest.)  I
figure that 50M is about 341 seconds out of the 650M = 74 minutes, so
this works out to a read speed of 9.2x

On my external scsi 16x drive I did:

  time dd if=/dev/scd0 of=/dev/null bs=5k count=10000

To read 50M it took 48 seconds, which works out to 7.1x.  (This
block size seemed to be the fastest.)

These timings don't seem consistent with the advertised ratings.  Is
this normal?  Is there something I can do to speed them up?

Thanks for any help,


Dan Christensen

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