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dd is slow after 1.5 gigs ??  using dd if=/dev/cciss/c0d0p1 of=/usbdrive/test.img

computerfixins
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Last Modified: 2008-01-09
Hello experts,

Trying to make an image file from a parition and then write it to a usb drive.  I will later mount the image file using the -o loop (loopback interface).

So basically my command looks like

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

For some reason as soon as the file hits 1.5gigs, the thing slows down to a crawl...  I barely get .2 megs/sec transfers rates.

The USB interfaces are both usb 2.0 high speed.  Should be blazing along at +20MB/s not almost .5 ?

thanks!

-jc
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system administrator
Top Expert 2007
Commented:
Hello.
Try to lower bs to 64k and tell me what happens

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XoF
Commented:
Sure you're talking 'bout Linux? The device names looks like BSD...
Anyway, how many RAM does your box have? Could it be, that the first 1,5 Gigs are getting cached in RAM?

-XoF-

Author

Commented:
running on a hp dl585 with 4 cpu's and 8+ gigs o ram.

Using Linux Advanced Server 4.0 and 2.1  

The cciss/c0d0p1 is a partition on a RAID5 set.

Will try the 64k block size now.

Author

Commented:
er; thats redhat linux advanced server or better known as LAS

Author

Commented:
64k yielded same results, fast until 1,480,000,000(10-20 MB/second)

Then it starts averaging a little less then 1MB/second.  

I'm going try cp the data over, see if its actaully dd thats doing it.
CERTIFIED EXPERT
Most Valuable Expert 2015
Commented:
Have you tried using partimage instead of dd?

Author

Commented:
will try tonite, does partimage make a mountable image file?
CERTIFIED EXPERT
Most Valuable Expert 2015

Commented:
I haven't needed to mount it but I think it is probably similar to what you get with dd.

Author

Commented:
bah, darn thing was tricking, after some long hours of banging my head on the wall i read up on the hole ohci, uhci, ehci.  Realized that my kernel is running 2.4.9.  Which means only usb 1.1 is supported...  

Guess I need complile a new kernel... ugh...
Artysystem administrator
Top Expert 2007

Commented:
:-)
This may not help.
Do you think 1,5 Gigs are buffered and only then are really written to USB drive?
If so, you are lucky and USB 2.0 helps, if not, the problem will repeat.
Also you USB port may not be 2.0 compliant.

lsusb -vv (from root may help).
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