[Nottingham] Writing into FLASH!

[Martin]

Martin wrote:
[---]
> 
> time cmp -l mandriva-linux-free-rc2-2010-x86_64.iso /dev/sdf
> 
> cmp: EOF on mandriva-linux-free-rc2-2010-x86_64.iso
> 
> 14:04.33 elapsed 0% CPU
> 
> which is to be expected being as the memory stick is larger than the iso 
> file.
> 
> 
> Curiously, that timing equates to only approximately 3.5MByte/s. I guess 
> the double buffering and blocksize makes a difference on reads also.

Even more curiously, from a few more runs to test the read speeds...

The usb memory stick read speed appears to be about 5.4 MB/s for most of 
the tests with a sweet spot for 4kB block reads of 6.0 MB/s. There's a 
slight speedup for 1kB (and smaller) block reads going up to 6.5 MB/s at 
the expense of increased CPU time. At smaller than 64 Byte reads and the 
throughput slows down again.

I suspect that the memory cache in the OS is doing all the hard work to 
keep the throughput looking good for 1kB and below... So does that 
suggest a usb stick memory page size of perhaps 1kB or 2kB?

The "double buffering" using pipes of dd appears to have little effect 
on the reads. The HDD reads for the cmp showed brief 40 MB/s bursts.

I'll be trying a few further tests...


The grepped timings are attached for anyone interested. (Hope not too 
bad a chunk for those not interested.)

Cheers,
Martin

-- 
----------------
Martin Lomas
martin at ml1.co.uk
----------------
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: flash_readspeed_test02b
Url: http://mailman.lug.org.uk/pipermail/nottingham/attachments/20091016/88272cd2/attachment.txt