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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

 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 
 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 

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

# sudo hdparm -tT /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?

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2 Answers 2

up vote 1 down vote accepted

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
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I have tried 16M and 32M block sizes, it's around 980k bytes/sec, it's still slow. –  Xiè Jìléi Dec 23 '10 at 3:49

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.

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Well, set a 2M block size doesn't improve speed. Do you know how to clear the read cache (as opposed to flush the write cache by sync command), so I can have a test on different block sizes? –  Xiè Jìléi Dec 23 '10 at 2:20
Cycling the tray should clear all caches. –  SilverbackNet Dec 23 '10 at 2:21
Should I must cycling the tray? My test script is: for bs in 4k 8k 16k 32k 64k 128k 256k 512k 1M 2M 4M 8M 16M 32M 64M; do sync; echo block size: $bs; /bin/dd if=/dev/sr0 of=m.iso bs=$bs count=30; done –  Xiè Jìléi Dec 23 '10 at 2:23
eject can open and close the tray. (Different drives respond differently, try -r, -t, and -T.) There is probably another way to dump the cache, I just don't know it. –  SilverbackNet Dec 23 '10 at 2:30
No, eject doesn't close the tray on laptop. –  Xiè Jìléi Dec 23 '10 at 3:16

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