[CentOS] Shrinking a volume group

Steve Bergman steve at rueb.com
Thu Sep 14 00:27:46 UTC 2006

On Wed, 2006-09-13 at 13:06 -0400, William L. Maltby wrote:
> The problem in the current discussions, IMO, is that the tunability of
> the original *IX (rife with high and low water marks for cache, swap
> activity, text, data, I/O of various types, ...) could satisfy the
> needs
> of admins willing to learn it, but was considered too "complex" by the
> community at large (that is, those who paid for it all - business)
> because they had a hard time finding the expertise and paying the
> price
> demanded by that expertise. 

I've always been rather skeptical of the claim that smart admins could
analyze their "workload" and tune the system based upon their keen
understanding of what the appropriate watermarks should be.

What is the "workload" for a multi-user desktop server?  What is the
proper high watermark for a system when it's 12:30pm CST and everyone is
at lunch, except for Charlie, who decided to stay late to run his daily
reports.  Or maybe Charlie was sick that day, and Angela ran them, right
at 5pm.  (Oops! I almost forgot!)

Of course, Veronica always does End Of Day at 5PM.  And she complains
that something was wrong with the system "yesterday".

Hank and his crew usually come in at 8.  But he was under a deadline and
had his guys working on reports in OpenOffice from 7am on so that his
department could meet the deadline at noon.  (Tony prefers Gnumeric.
Tina refuses to work in anything but Microsoft word via X-Over Office.
And yes, I recommended against that but the General Manager over-ruled

It's not that admins aren't smart enough, these days.

It's that it's just plain silly to think that a human being could tune
for these things.

There is no such thing as a "workload" to be tuned for.  Every time I
see that word, I have to laugh.  Because it doesn't exist.

Perhaps on a large enough system, an admin can reasonably treat a
workload as a statistical entity, ala thermodynamics.

But CS equations are never going to be as neat as thermodynamic ones.
So it just means that when the hammer falls, it's just going to be that
much more impossible to deal with.

The system really needs to tune itself dynamically.

I know that you are saying that we can't go back to the days of manual
tuning.  And I agree.  But for different reasons, I think.

It's not that admins aren't smart enough, these days.

It's that they never were...


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