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

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 ?


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Try to lower bs to 64k and tell me what happens

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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?

computerfixinsAuthor 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.
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computerfixinsAuthor Commented:
er; thats redhat linux advanced server or better known as LAS
computerfixinsAuthor 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.
Have you tried using partimage instead of dd?
computerfixinsAuthor Commented:
will try tonite, does partimage make a mountable image file?
I haven't needed to mount it but I think it is probably similar to what you get with dd.
computerfixinsAuthor 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...
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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