Re: Determining disk activity per volume
Re: Determining disk activity per volume
- Subject: Re: Determining disk activity per volume
- From: Michael Smith <email@hidden>
- Date: Sat, 7 Oct 2006 13:33:02 -0700
On Oct 7, 2006, at 10:51 AM, Rick Mann wrote:
On Oct 7, 2006, at 01:59 , Michael Smith wrote:
No, it will work very badly. Please look at the iostat code I
referenced yesterday. If you don't follow my advice, please at
least let us know the name of your product so that I can avoid it
like the plague.
Perhaps you can elaborate? I did take a look at iostat, and since
it wasn't immediately obvious what it was doing, and I saw the
Kauth solution at about the same time, I chose that instead.
Maybe if you can explain why that's such a bad approach, I'll
reconsider.
The kauth hooks were designed for code that needs to be on the hot
path; either because it is actively participating in the process of
authorising filesystem operations, or because it hooks into an
external queueing mechanism that requires precise notification of
operations.
Your application does not participate in authorisation, and it does
not require precise notification. From reading your messages, it's
clear that you have little or no understanding of the consequences of
injecting code on the hot path:
I believe the approach I'm looking at now, Kauth, will miss
requests satisfied by the cache.
Kauth sits on the application side of the I/O stack, but it only
covers authorisable operations. These have no direct relationship
with disk I/O.
I looked at iostat's code again. I see that it asks the OS for
device statistics, but I don't see how that helps me to implement a
disk activity indicator. I want to display, within a humanly-
imperceptible delay period, an indication that a read or write had
begun or ended.
Perhaps you could explain what you mean by "a write has begun or ended"?
My Mac workstation here at home has a disk subsystem capable of
around 15,000 IO/sec. What sort of "notification" do you intend to
display to the user that each of those I/Os has "begun" or "ended"?
= Mike
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