Re: [dm-crypt] Improving performance?

[Arno Wagner <arno@wagner.name>]

Hi Lasse,

have you done any benchmarks for kcryptd to determine the 
bottleneck is your CPU? My intuition would be that for this
setup and the stated speed it is likely, but better be sure
than to optimize nthe wrong parameter.

As to options, basically a faster CPU and/or more cores 
is one, the other is SSD, if the bottleneck is with the
disks. A third one is a different controller and/or
bus attachment of the controller. It is also possible
that a singel disk slows things down. HDDs can get donw
to 50% of the start-of-disk speed somehwere between the
50% coapacity mark and the end.

The second thing you need to ask you, is if you are
only interessded in linear read speed. If not, an
increase 70 -> 100 may well be insigificant in the
access mix you are using and not worth the investment.

Gr"usse,
Arno



On Thu, Nov 11, 2010 at 11:49:16AM +0100, Lasse Jensen wrote:
> Hi. I have a RAID 5 array with 3 (soon upgrading to 4 + hotspare = 5)
> encrypted drives connected to a system with a Core 2 Duo @ 2.5 ghz  running
> Debian Squeeze.
> Each drive has been formatted with
> 
> cryptsetup luksFormat /path/to/device
> 
> And put together in a array with
> 
> mdamd -C /dev/md0 --raid-level=5 /path/to/first-device /path/to/third-device
> /path/to/third-device
> 
> It works great, and encrypting the devices separately allows me to run more
> than one instance of kcryptd, thus using both cores in my server. It
> compensates for the overhead of encrypting the checksumming data seperately,
> compared to raw devices -> RAID -> encryption and still give me improved
> speed.
> 
> At the moment, i get 70 mb/s sequential read speed locally. I would like to
> boost it to at least 100 or even more, as 1) the raw drives support way more
> and 2) i would like to fill my gigabit ethernet when copying files over the
> network.
> 
> Now, what are my options?
> 
> A quadcore CPU like the Q6600 would double the number of cores and
> theoretically double the throughput, but at cost of idle power. Note that
> the server is idle most of the time.
> A core i5. They have AES support in hardware, but it's an expensive solution
> and i'm not even sure it has Linux support.
> A PCI or PCIe based card, like the HiFN cards, but what card should i look
> for and what speed should i expect?
> Using the CUDA cores of my nVidia card, but no driver seems to exists for
> that.
> 
> The first option is pretty straight forward, but what about the rest? Or are
> there any other options i havent thought of?
> 
> -- 
> Lasse Jensen (fafler at gmail dot com)

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-- 
Arno Wagner, Dr. sc. techn., Dipl. Inform., CISSP -- Email: arno@wagner.name 
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