dd is very slow? Any alts? suggestions?

zerobane · 03-20-2006, 10:08 AM

Hellos,

Using dd to copy some data from a drive to a image file on a usb device.

I am averaging about 1/2 meg a second, I was wondering if anyone could shed some light on what the bottleneck is and if a workaround is possible.

Is there any other way of making an image file of a partion?

dd if=/dev/c0d0p1 of=/mnt/usbdrive/test_image.img

Drive / usb are both 2.0 high-speed devices.

ntubski · 03-20-2006, 10:53 AM

Try playing around with the bs option eg:

dd if=/dev/c0d0p1 of=/mnt/usbdrive/test_image.img bs=4M

Dragineez · 03-20-2006, 02:56 PM

If they're both USB devices, then they're both using the same bus. Yes, it will slow down some.

zerobane · 03-20-2006, 03:11 PM

dev/c0d0p1 is on a U320 RAID 5.

the usb is a 2.0 high speed device, in theory I should be getting 30+MB/s? 480mb/s rated...

instead it takes about 30 seconds to do 1.5 gigs, then it take 2+ hours to finish the rest. (on a 10 gig partition)

this is running on a proliant dl585 with 4 cpu's and 8+ gigs of ram...

ntubski · 03-20-2006, 03:46 PM

I don't really know all that much about the hardware aspects of it, but it occurs to me that you probably want a compressed image, and writing a smaller file will be quicker.

dd if=/dev/c0d0p1 | gzip >/mnt/usbdrive/test_image.img.gz

Also did you try using the bs option?

zerobane · 03-20-2006, 03:55 PM

just got done using the bs= opition, tested a range from 1M-100M. Seems to make a difference up until its gets to 1.5 gigs. As soon as the image file becomes 1.5 gigs the dd command goes from 10-30% cpu to 1%-2% and begins to spit out around .1 to .2 Megs/s.

I will be later mounting the images using the loopback interface, so i want to avoid zipping.