[K12OSN] USB v2.0 HD throughput

John Lucas mrjohnlucas at gmail.com
Mon Mar 5 11:01:55 UTC 2007

I recently bought a 500GB SimpleTech USB hard drive to back up my three home
Linux machines. After ridding the drive of the NTFS filesystem and replacing
it with an ext2 filesystem with "parted", I started backing up the data
folders on my new laptop (home directory, photos, music etc.). The throuhput
was dismally slow.

After some experimentation I discovered that the bottleneck was the KDE
"kio_slave" process (my normal desktop is KDE). Below are the results of three
quicky "benchmarks": copying the same 170MB ISO file from the system drive to
the USB drive. All runs were on the same computer to the same locations.

The results of this are interesting: KDE was by far the worst performer, Gnome
is much faster, but for pure performance, always go through the regular kernel
filesystem. The "kernel I/O" was acheived by mounting the drive the old
fashioned way, rather than relying on the desktop managers: 

	mount /dev/sdb1 /mnt/usb 

	KDE I/O throughput:	 1.75Mbytes/sec.
	Gnome I/O throughput:	17Mbytes/sec.
	Kernel I/O throughput:	25Mbytes/sec.

Timings need to include flushing the I/O buffers, so "sync" times
are added to copy times for the calculations.


jlucas at toto ISO]$ time cp olpc-livecd.iso /media/disk/Toto ; time sync

real    1m37.295s
user    0m0.041s
sys     0m3.290s

real    0m0.007s
user    0m0.000s
sys     0m0.002s

Gnome I/O

[jlucas at toto ISO]$ time cp olpc-livecd.iso /media/disk/Toto ; time sync

real    0m6.068s
user    0m0.028s
sys     0m0.653s

real    0m4.012s
user    0m0.000s
sys     0m0.003s

Kernel I/O

[jlucas at toto ISO]$ time cp olpc-livecd.iso /mnt/usb/Toto ; time sync

real    0m0.360s
user    0m0.064s
sys     0m0.292s

real    0m6.400s
user    0m0.000s
sys     0m0.058s

        "History doesn't repeat itself; at best it rhymes."
                        - Mark Twain

| John Lucas                          MrJohnLucas at gmail.com               |
| St. Thomas, VI 00802                http://mrjohnlucas.googlepages.com/ |
| 18.3°N, 65°W                        AST (UTC-4)                         |

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