Emmanuel Briot wrote:
What makes disk filesystems slow is not the code run on
the CPU...it's the operating speed of the disk-head
actuator.
It's not the filesystem that's slow, it's the DISK DRIVES
that are slow.
The disk I/O bottleneck is not the CPU overhead , it's the
speed which the read/write head can be placed into the proper
track position plus additional waiting for the correct sector
to come around underneath the read/write head.
There are not "slow" filesystems, only slow hard disks.
You have never used Windows, I guess. Its file system is much slower
than any of those on linux, using the same disk (dual-booting).
I'm all too familiar with Windows. What makes it the MS filesystems
slow is, again, disk head movement. MS filesystems have very
inefficient disk-head movement patterns.
Now, if you can answer the question on what tools exist to simulate a
slow hard-disk if you wish, that would be extremely interesting. That
would be, I guess, a user-side file system that introduces explicit
delays.
Now, Dave's proposal of using NFS is indeed what I have been doing so
far, but nowadays local network become so fast that the difference is
not that big. All I want here is to be able to slow down the
application while monitoring it in a profiler, which would help find
out what parts of the application are slow.
I'll investigate the "rsize=1, wsize=1" parameters, which I do not know
about.
Personally, I think you'll get a "slow" filesystem, but that
your data is not going to correlate very well with whatever
you're modelling.
If you want to test a "slow" filesystem, then just create
and mount that type of filesystem, and do some I/O on it.
Anything else is just mental masturbation (and if the date
is going to be used for marketing purposes...fraudulent).
Emmanuel
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