Copy from CDROM is very slow in Ubuntu

Question

I'm using the command to copy CDROM image:

# dd if=/dev/sr0 of=./maverick.iso

But it's very slow, at about 350k bytes/sec. I've searched the google, and try the command

# hdparm -vi /dev/sr0

/dev/sr0:
 HDIO_DRIVE_CMD(identify) failed: Bad address
 IO_support    =  1 (32-bit)
 readonly      =  0 (off)
 readahead     = 256 (on)
 HDIO_GETGEO failed: Inappropriate ioctl for device

 Model=DVD-ROM UJDA775, FwRev=DA03, SerialNo=
 Config={ Fixed Removeable DTR<=5Mbs DTR>10Mbs nonMagnetic }
 RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0
 BuffType=unknown, BuffSize=unknown, MaxMultSect=0
 (maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0
 IORDY=yes, tPIO={min:180,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4 
 DMA modes:  sdma0 sdma1 sdma2 mdma0 mdma1 mdma2 
 UDMA modes: udma0 udma1 *udma2 
 AdvancedPM=no
 Drive conforms to: ATA/ATAPI-5 T13 1321D revision 3:  ATA/ATAPI-1,2,3,4,5

 * signifies the current active mode

Seems like DMA is already on.

And a device test gives:

# hdparm -t /dev/sr0 

/dev/sr0:
 Timing buffered disk reads:    2 MB in  6.58 seconds = 311.10 kB/sec

# sudo hdparm -tT /dev/sr0 

/dev/sr0:
 Timing cached reads:     2 MB in  2.69 seconds = 760.96 kB/sec
 Timing buffered disk reads:  m  4 MB in  5.19 seconds = 789.09 kB/sec

The CD-ROM device and disc should be okay because I can copy it very fast in Windows, using UltraISO utility.

So I guess there is something not configured right in Ubuntu, is it?

Answer 1

You're using dd incorrectly.

The block size for dd is 512 bytes by default, which is acceptable (but not great, more on that later) for a hard drive since hard drive sectors are 512 bytes in size. CD-ROMs, however, have a sector size of between 2048 and 2352 bytes. The default block size causes the drive to do four or five partial reads per sector, slowing it down immensely.

The other things to factor in are the access timing and the drive buffer. To make a long story short, instead of reading sector-by-sector, you should read large chunks. I don't know what the buffer size of the drive is, but 32 megabytes is generally a decent block size.

# dd if=/dev/sr0 of=./maverick.iso bs=32M

Answer 2

It's on UDMA2, so there should be nothing to configure. It might be more simple than that: Have you tried using bs=2M on your dd command? (You might have to try a few to find the optimal size for CD-ROM, if it gets too large the CD will spin down. dd doesn't use overlapped i/o.) Longer reads should get faster.