Thread: Disk writes

> I could I discover who is sending so many data to the disks?

Documentation/laptop-mode.txt in the Linux kernel tree has some
instructions how to track down unwanted disk writes.

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Florian Weimer                <fweimer@bfk.de>
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On Thu, 2006-07-27 at 20:25, carlosreimer wrote:
> Hi,
>
> We've a fedora core 3 box with PostgreSQL 8.0.
>
> There is some performance problems with the server and I discovered
> with vmstat tool that there is some process writing a lot of
> information in the disk subsystem.
>
> I stopped the database and even so vmstat showed the same rates of
> disk writes.
>
> I could I discover who is sending so many data to the disks?

Does top show any processes running?

On my FC4 laptop, the one that kept cranking up all the time was
prelink.  I don't really care if it takes an extra couple seconds for an
app to open each time, so I disabled that.

The other process I've seen do this, on older flavors of linux mostly,
is kswapd erroneously writing and reading the swap partition a lot.
Seems to happen when the swap partition is smaller than physical memory,
and there's a lot of other I/O going on.  But I think that got fixed in
the 2.6 kernel tree.

Hi, Reimer,

carlosreimer wrote:

> There is some performance problems with the server and I discovered with
> vmstat tool that there is some process writing a lot of information in
> the disk subsystem.
[..]
> I could I discover who is sending so many data to the disks?

It could be something triggered by your crontab (updatedb comes in my
mind, or texpire from leafnode etc.).

Another idea would be that you have statement logging on, or something
else that produces lots of kernel or syslog messages[1], and your
syslogd is configured to sync() after every line...

HTH,
Markus

[1] We once had such a problem because an ill-compiled kernel having USB
verbose logging on...
--
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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