Comment 158 for bug 197762

man, 08 06 2009 kl. 20:14 +0000, skrev epv:
> This isn't normal behavior. Obviously it behaves fine while all writes
> are going to buffer cache, but once it tries to write it out to the
> device, wait times on the partition shoot up to 30sec or more, and all
> processes trying to touch the usb disk block practically forever.

If other processes get completely starved due to the writeout then there
is probably something in the VM, file system or I/O scheduler that needs
to be fixed. You would have to make a convincing argument, though, like
providing a very simple usecase. It should literally be something as
simple as the following

(cp bigfile /media/disk/ &) ; sleep 10 ; time echo foo > /media/disk/bar

If the time is really in seconds as you seem to suggest it is
interesting I'd say. On the other hand, if what you describe is due the
low performance of the underlying device then it is expected behaviour
(the low performance of the device might be due to a bug though).

> Sysstat shows it as 100% busy continuously.

'It' being the underlying device? That is what you would expect.

> The reports of "Fast at
> first, then slowing down" are of course because of the buffer cache
> making it look like it's initially "fast" but access to the underlying
> device is always very slow, whether you are writing to it with gvfs, cp,
> dd, buffer, or whatever.

Yes, and?

> In addition, it's only writes that are slow, and they're vastly slower
> than could be explained by a crappy USB device- in my case around 100 -
> 200 kbytes/sec on a device that under a Hardy install writes at several
> mbytes/sec.

If Hardy was fine then you should open a new bug report with the proper
details (once again, see [1] or Theodore's comments).

[1] https://help.ubuntu.com/community/DiskPerformance