Re: ciss(4): speed degradation for Compaq Smart Array [edited]

From: Chuck Swiger (cswiger_at_mac.com)
Date: 03/30/05

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    Date: Wed, 30 Mar 2005 15:37:06 -0500
To: Martin Nilsson <martin@gneto.com>

    Martin Nilsson wrote:
    [ ... ]
    > What is wrong with using dd to measure max read/write bandwith of the
    > controller-disk system?

    Nothing-- it's fine. There are people around here who have very strong
    viewpoints with regard to accurate, reproducable testing. Their suggestions
    are worth paying attention to, but there is some level of nitpicking going on
    about just what it is you're testing when you run such-and-such a command.

    > On a modern disk this should give numbers in the vicinity of 50MB/s at
    > the beginning of the disk. This tells me in seconds if there is
    > something wrong with the controller, cable, disk (or FreeBSD driver).

    Absolutely, you're doing a sanity check on the hardware, and seeing whether
    the numbers are roughly what they should be.

    The difference between a scientist and an engineer is that the latter
    *doesn't* want to reproduce the sparks when something shorts out just to
    obtain a standard deviation. 

    -- 
-Chuck
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