[dm-crypt] unusual writing speeds when benchmark speeds are high enough

Matthias Schniedermeyer ms at citd.de
Mon Mar 18 09:37:00 CET 2013

On 18.03.2013 02:42, .. ink .. wrote:
> I would say, there are quite a few details missing.
> > Hardware, Software?
> > 28.4 MB/s also isn't what i would call fast, what is that?
> >
> > The person responded and this is his computer spec:
> intel core 2 duo e8500
> 2 gb ram
> 2x 80 GB HDD western digital 7,200 RPM
> Kernel 3.2.18-pclos3.bfq
> 32bit os
> No LVM volume or RAID stuff,the test was done from the user home directory.
> What speed do you get from "dd" command?. People usually say the speeds i
> post are not high enough but  i do not remember anybody saying what speeds
> are normal,expected.

My newest acquisition (got it friday), a 7200RPM HDD, does between 
190MB/s (outer rim) and 90MB/s (inner rim).
The performance i got out of it yesterday, when i tried the dd command, 
was 137MB/s (and 3.1 GB/s for the version without conv=fsync).

The HDD before that, a "green" model with around 5400 RPM, does between 
130MB/s and 60MB/s.
The best performance i usually see in reality is about 110MB/s, but it 
depends on where the files are written to and also where the source-file 
was placed on the source-HDD, so in the worst-case is about 60MB/s.

The SSD i have can reach (with encryption) about 400MB/s, but that is 
best-case performance when all moons are aligned. I haven't really 
benchmarked the real-world performance, the dd-example (with conv=fsync) 
only got 88MB/s.



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