[Soekris] Harddisk Slow

[Michael Stone]

On Wed, Jan 31, 2007 at 02:48:11PM +0100, Igor Sobrado wrote:
>A block size of 1MB means that the even small scripts (e.g., a 600 bytes
>shell script) will require 128KB to be stored.

Umm, the dd block size has absolutely nothing to do with what is stored 
on the disk. Instead, it is the size of the read or write request that 
dd sends to the kernel. A larger block size may result in more efficient 
use of the disk (although modern kernels can readahead an nullify that 
effect to some degree) and will result in fewer system calls to transfer 
the same amount of data (a big factor on a relatively slow system like 
the soekris). The sweet spot on a single drive is usually something like 
16-64k, beyond which performance might actually decrease because the 
request may need to be broken up before being sent to the disk. But, 
again, this has absolutely nothing to do with how things are actually 
laid out on the disk. (It is possible that you can get a slight 
performance advantage if the block sizes are tuned based on the physical 
disk layout, but on a single disk in a soekris that really doesn't 
matter.  Also, if you're using dd with a tape the block size is very 
important, and does impact the physical layout of the tape, but again 
that's not relevant in this case.)

>DMA modes (in most cases, UltraDMA 2) why is the interrupt load so high?

Because the soekris boxes are not designed for IO intensive operations 
and tend to have a relatively high interrupt load for any kind of IO 
(including USB or network).

>I am using a PowerEdge 350 here.  It can easily provide 20MB/s with
>an 800MHz PIII procesor.  The net4801 has a relatively fast Geode
>processor (266 MHz is not too slow).  Even my 400MHz PII laptop
>is faster than the net4801 in both writing and reading:

Well, would you expect otherwise than that an 800MHz PIII or a 400MHz 
PII are faster than a 266MHz geode? Not only are they clocked faster, 
they're also using faster memory, faster busses, architectures which can 
sustain more operations per cycle, and they draw an order of magnitude 
more power. It's actually a testament to the architecture that it's as 
competitive as it is; there are tradeoffs in any system design, and the 
soekris boxes are designed to be very low power devices, not database 
servers.  If you need high IO numbers you need to look at a different 
device, period.

Mike Stone