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odd speed variation in dd between ubuntu and windows

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stewztheone
(@stewztheone)
Posts: 2
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Topic starter
 

Hey all - I am trying to get to the bottom of a speed / throughput issue with DD. (Using the same laptop and hardware)

If i run the Helix 2009 R3 Live in Linux mode and DD sata USB -> sata USB with a bs of 2K I am getting a speed of 10M/s.

If I boot into Helix response under windows (7) and use DD in the same configuration I get about 10M/s.

Now, the difference is that in Linux, after around 30 mins 10 goes down to 9, then all the way down to around 1.5 M/s after 2 hrs of imaging.

In Windows it states constant at 10 M/s and my 240GB drive is done in around 4 hours.

Any idea what is causing this?

Thx

 
Posted : 14/05/2010 7:58 pm
(@rampage)
Posts: 354
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EDIT
mhh you mean that helix live imaging a disk is slower?

sounds strange.
have you tried using a different distribution? like deft or caine?

 
Posted : 15/05/2010 1:29 am
stewztheone
(@stewztheone)
Posts: 2
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Topic starter
 

What I mean is when I used DD from in linux from any distribution, I start fast and end slow. When I use windows DD or Helix Pro under windows I have fast throughput from start to finish.

I though it was a hardware issue at first as I was just working in Linux, but once I tried in Windows everything was fine.

Now I am trying to figure out what config, setting, library in linux is causing the slowdown over time.

I have tried Helix, plain ubuntu, plain debian, all with the same outcome. Start around 10 M/s end very slow, sometimes around 500 k/s

I use the same hardware/disks/cables/etc each time.

 
Posted : 15/05/2010 8:42 pm
(@xaberx)
Posts: 105
Estimable Member
 

What I mean is when I used DD from in linux from any distribution, I start fast and end slow. When I use windows DD or Helix Pro under windows I have fast throughput from start to finish.

I though it was a hardware issue at first as I was just working in Linux, but once I tried in Windows everything was fine.

Now I am trying to figure out what config, setting, library in linux is causing the slowdown over time.

I have tried Helix, plain ubuntu, plain debian, all with the same outcome. Start around 10 M/s end very slow, sometimes around 500 k/s

I use the same hardware/disks/cables/etc each time.

I'm not sure for the difference in the linux to windows, however there are many ports of dd to windows. Some are faster than others, for example dcfldd is not as fast as one from chrysocome.net on certain media types like flash…not sure why just from testing i have found this out. I do not know what port Helix uses for its imaging process perhaps it is a different port of dd that is more efficient/ revised than the internally installed version.

 
Posted : 01/11/2010 1:49 am
(@hardcore)
Posts: 5
Active Member
 

Couple of things to try

1. try increasing the physical memory.
2. you did not say where you were imaging to, are you imaging to the linux system drive.
It may be that the swap-space is causing disk seeks which are degrading the image seeks when writing the file.

 
Posted : 01/11/2010 5:43 am
Beetle
(@beetle)
Posts: 318
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If you could post the command you are using (and if different on each platform) that would be helpful to see what might be happening.

 
Posted : 01/11/2010 6:38 am
(@joachimm)
Posts: 181
Estimable Member
 

Any idea what is causing this?

Multiple things can cause speed variations (see below). But often they are not that significant as the one you are describing.

What FS are you writing to on both systems ? E.g. NTFS3g might be slower on Linux. Another possibility is that some faulty code is causing it.

Have looked at the system state during in the 1.5 MB/s period, i.e. free (overall memory usage), iostat (IO statitics), vmstat (Virtual Memory/Paging statistics), top (specific process information), etc.

Does the same speed variation occurs with another imaging tool e.g. ewfacquire?

Other possible speed variation causes.
* overhead operating system/file system/hardware drives
* caching/read ahead by operating system
* optimization of the executable, compile and runtime
* other processes consuming IO/CPU time
* memory management/swapping
* Different versions of dd
* Difference in how the speed is measured (see below)

Approach 1 (measured speed of the pipeline)
determine start time
for all data
read data
write data
calculate speed using start time
determine completion time/overall speed

Approach 2

for all data (measured speed of the read)
determine start time
read data
calculate speed using start time
add delta to completion time/overall speed
write data

Joachim

 
Posted : 01/11/2010 12:23 pm
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