Ulrich --- if you have time to try to do more tests, may I gently
suggest that you start a new Launchpad bug? Drop a pointer from in
this launchpad bug number to the new one, but let's do all of the
experimentation on a new launchpad bug. There are a couple of reasons
for this:
(1) Launchpad has horrific scalability problems, and it's painfully
slow to find new entries on this Launchpad entry, since it has so many
comments already.
(2) It's not clear everyone on this bug is sufferring from the same
bug. They may have similar symptoms, but that doesn't mean it is the
same bug. It's actually **highly** confusing to have many people
glomming on with a "me, too!!" comment, giving a very tiny amount of
information, but not actually giving a full description of what they are
seeing. In fact, the tiny amounts of data may be horribly misleading,
because they may be seeing a different bug.
(3) As a result, many kernel developers on LKML don't spend a lot of
time on Launchpad bugs; the bug reporting is ___so___ ___bad___ that
it's just too frustrating and time-consuming for them. And
unfortunately, Canonical has a fairly limited kernel team, and it takes
them a lot of time try to synthesize a good bug report from a lousy one.
In fact, someone recently posted this bug report on LKML, and what it
mostly got was a vent from someone complaining how useless most Ubuntu
bugs were. (Well, it also got me interested enough to actually take a
look, but I've gotten inured to how lousy Ubuntu bug reporting
infrastructure is for large bugs, as well as mostly uninformative bug
reports.)
So if we do have one or more people who have the time and energy to do
some real bug reporting (which takes real work), may suggest that each
person open a separate bug, and each bug, give (a) full details about
what kernel version, including whether it is a Ubuntu kernel or a
mainline kernel, (b) full details about your hardware version, including
which disks are hooked up which way (i.e., eSATA, USB, SATA, PATA,
etc.), and (c) exhaustive details about how you ran your test case,
whether or not is repeatable, etc. Also note that it is an instance of
Launchpad bug #197762, and that anybody else who wants to glom on with a
"me, too" is kindly asked to put that remark in the #197762
cesspit^H^H^H^H^H^H^H^Htop-level bug, and not in the new bug report,
which we can hopefully keep specific to your situation.
I would again suggest that you try doing multiple tests:
1) Copying one file from one disk to another
2) Copying from /dev/zero to file on the disk
3) Copying from /dev/zero to the raw disk device (yes, this will blow away
your filesystem; hopefully you have scratch devices)
The ideal bug reporter will have multiple devices that can be attached
via different hardware interfaces (i.e., eSATA, USB, maybe a spare SATA
port), so we can try to rule out hardware attachment problems.
If someone is willing to do all of that, I'm more than willing to try to
drill down as far as I can; although if it turns out to be a USB
problem, I'll need to call in help from a USB developer ---- but with a
well constructed bug report, that shouldn't be a problem; I should be
able to overcome LKML prejudices about lousy Launchpad bugs ("no really,
this one is different; we've kept it clean and professional, and there's
plenty of information --- and we have a technically cluefull user who is
willing to work with you and run experiments until the problem can be
solved")
More generally, maybe someone with the time can start a Wiki page on
debugging filesystem performance problems, maybe on the Ubuntu wiki
somewhere, or on ext4.wiki.kernel.org. There are plenty of tools like
that people can use for debugging performance problems, beyond just
"dstat". Other tools include blktrace, sar, iostat, vmstat, and many
others. Launchpad is really a lousy place to have these discussions; a
wiki or a forum topic is really much better.
--
file transfers on USB disk are very slow
https://bugs.launchpad.net/bugs/197762
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