# dd copy - how long?



## jauburn (May 18, 2006)

I'm doing a dd copy of one 400 GB drive to another. 27 hours so far, and no idea when it will be done. Anyone done this?


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## spankspank (Nov 7, 2000)

jauburn said:


> I'm doing a dd copy of one 400 GB drive to another. 27 hours so far, and no idea when it will be done. Anyone done this?


It depends on the speed of the PC you are using and the size of the disk. Is the drive light still blinking? I could see a 400G drive taking more than 27 hours on a 500Mhz PC.


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## wscannell (Dec 7, 2003)

If DMA is turned on, it should do about 1GB a minute if the two drives are on different IDE controllers. It is possible that DMA is not turned on, so it may take significantly longer. Not really sure how long, but I would wait at least overnight again.


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## MichaelK (Jan 10, 2002)

is there a way to tell if DMA is turned on or not?

And if not, can you turn it on?


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## wscannell (Dec 7, 2003)

To turn on DMA:

hdparm -d1 /dev/hdX

Repeat the command for each hard drive that you are using (substitute hdX with the proper hard drive name.)


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## spankspank (Nov 7, 2000)

MichaelK said:


> is there a way to tell if DMA is turned on or not?
> 
> And if not, can you turn it on?


The command:

hdparm /dev/hdX

will tell you if DMA is on for that drive. If DMA is off then other important parameters are probably not optimal either.

I would recommend using:

hdparm -d1 -c3 -m16 /dev/hdX

to turn on DMA, set 32bit IO_support, and 16 sectors transfers (multcount). Run this on both source and destination drives which should be on separate controllers. Optimizing everything can increase performance considerably.

These setting are good for almost all hardware in use today. Given the negative impact on disk performance, why do CD based distro not make this the default? Wouldn't this only fail on 386 and 486 computers?

More hdparm tips:

1. hdparm offers a simple way to predict how long your dd copy will take if the disks are on separate controllers. Run this before you start copying, substitue X for your source drive letter.

hdparm -t /dev/hdX

2. You can however change ide settings with hdparm after starting the dd copy, it won't corrupt or stop the transfer - it will speed up the remaining job.

3. This command:

hdparm -I /dev/hdX

will tell you quite a bit about your hard drive's capabilities.


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## viper36 (Mar 19, 2002)

I just completed a dd of a 250gb drive and it took over 36 hours.


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## MichaelK (Jan 10, 2002)

that's uglly...


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## lkinley (Mar 28, 2002)

Perhaps setting the blocksize (via bs=X) to something higher than the default (512 bytes) would speed things up?

-Lance


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