[rescue] Sun 711

[James Lockwood]

On Thu, 2 May 2002, David Passmore wrote:

> For large sequential reads the storage subsystem, sometimes the filesystem,
> and the drives themselves (drives have no battery-backing thus their caches
> are purely read cache) will read-ahead several sectors, tracks, or even
> entire cylinders-- since the platters rotate under the heads once for either
> one sector, track, or a cylinder (only very high-end drives can activate
> more than one head at a time), might as well read it all. This is why read

Anyone else remember the dual-head Eagles?  Ancient history, but they were
pretty neat.

> I use a combination of Solaris TNF tracing to profile an application's
> storage access, and a Veritas utility called vxbench to generate simulated
> loads. TNF tracing is very useful for many other things as well.

Let me second this.  TNF probes have to be some of the most useful Unix
kernel profiling hooks out there.

I also use some small libc shims to trace I/O, this can be very useful for
identifying pathological application behaviour.

-James