F16 unusable while writing to pendrive [SOLVED -- not]

[Patrick O'Callaghan]

On Mon, 2012-01-23 at 03:25 +0000, Marko Vojinovic wrote:
> On Monday 23 January 2012 02:41:07 you wrote:
> > Now I'll see how USB is going to work --- a 2.2 GB file is about to be
> > written... ;-)
> 
> As a side note --- is it normal to have the write-to-USB-flash speed of
> 2.5 MiB/s (on average)?
> 
> I am supposedly using USB2.0 port, and have a 8 GB flash drive. Writing a file 
> of 2.2 GB in size takes around 15 minutes to complete. Also that KDE progress-
> bar thing is reporting the 2.5 MiB/s value (on average) which fits my 
> calculation, but I was wondering if this is the expected performance or not.

I'd say that seems on the slow side, but there are several factors that
can affect it. For one thing, not all flash drives are created equal.
Even if they're supposed to work at USB2 speed, that's just the bus
speed of getting the data across the wire and doesn't really tell you
much. Cheaper drives are definitely slower than more expensive ones
which have larger internal buffers. Most commercial drives don't have
any published info on these speeds, but occasionally one sees
comparitive benchmarks being published (e.g. http://usbflashspeed.com/).

The other important factor is fragmentation. Even though flash drives
are theoretically random-access, the way flash memory works means that a
sparse distribution of blocks to be modified can make a large difference
to the effective write speed (see
http://en.wikipedia.org/wiki/Flash_memory#Limitations). This becomes
noticeable if you repeatedly create and delete randomly-sized large
files on the drive. In time the drive will become slower and slower
because of fragmentation, and it can sometimes make sense to copy the
entire contents, reformat the drive and copy the files back again in
order to "refresh" it. AFAIK there are filesystem designs which try to
minimize this effect, but I assume we're talking about VFAT here, as
it's the lowest common denominator for practical purposes.

poc