I/O performance/tweaking question

[guy keren]

did you try to break it down to sub-components?

i.e. on the source machine copy from the USB to a ramdisk - what's the 
sthroughput?

then try to write on the USB on the other machine from a ramdisk - 
what's the throughput?

then use netperf to check the throughput of the network between the two 
machines.

--guy

On 09/05/2012 11:51 PM, Oleg Goldshmidt wrote:
>
> Hi,
>
> I noticed something strange after upgrading two relatively aged
> computers from Fedora 14 to Fedora 17. Both 'puters are a few years
> old, one is a desktop, another a laptop. Both are connected to a
> vanilla home 802.11g wireless router, the desktop by cable, the laptop
> wirelessly. Each has an external USB disk attached (from time to
> time).
>
> Occasionally I copy files from one USB disk to another using scp or
> rsync - some files small, some large. I noticed long ago that copying
> over the network was faster than connecting both disks to the same
> computer, for whatever reason (single bus in both directions?). With
> the described setup I don't know what the bottleneck is - for all I
> know it may still be USB/disk if some buffer is kept full.
>
> What bothers me that after the upgrade the transfer speed went down
> markedly. When both 'puters were running Fedora 14 I typically got
> 2.3MB/s or even more. I was never surprised because the laptop has an
> Intel 5100 AGN wireless adapter that probably has 802.11n disabled (by
> default? not by me...), and if it is in 802.11g mode then I should
> expect less than 3MB/s, I think. However, with Fedora 17 on both ends
> it is always 1.0MB/s (e.g, as reported by scp). A transfer of a large
> file may start at 2.5MB/s but very rapidly converges to 1.0MB/s,
> occasionally fluctuating between 900KB/s and 1.1MB/s. Unattended
> backup through rsync is no problem, but when I copy something largish
> interactively it is much more annoying than before.
>
> I am surprised. Naively, I would expect a newer system to be at least
> as fast as the old one. Nothing but the Fedora version changed - same
> HW, the disks have not been reformatted, etc. I suspect that something
> may be optimized differently, but I have no idea what to tweak - or
> even what to check. Or mabe some obscure piece of firmware is missing?
> Does anyone have any suggestions?
>
> Obviously, I have no way to experiment with Fedora 14 anymore - it's
> gone.
>
> Thanks in advance for any suggestions.
>