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Date:      Wed, 18 Nov 2009 16:54:28 -0500
From:      Steve Bertrand <steve@ibctech.ca>
To:        Nerius Landys <nlandys@gmail.com>
Cc:        questions@freebsd.org
Subject:   Re: Measuring disk I/O
Message-ID:  <4B046D14.1070505@ibctech.ca>
In-Reply-To: <560f92640911181259m37d2659w775fa3fafd9499b6@mail.gmail.com>
References:  <560f92640911181259m37d2659w775fa3fafd9499b6@mail.gmail.com>

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Nerius Landys wrote:
> A friend and I are working on a small video-game related project as a
> hobby.  We're running several scripts 24/7 that make lots of calls to
> a MySQL database.  The mysql server process shows an average CPU use
> of 1% (reported by top) and it never goes above about 2%  The tables
> it's hitting are myisam tables.  I'm a little bit worried that the
> mysql process is using a lot of disk access.  I don't know too much
> about hard disks but my feeling is that too much disk use could slow
> the machine down or cause a premature hard disk failure.  WD Raptor
> model.
> 
> I don't know if my concerns are well-founded, but I would like to
> measure impact on the hard disk somehow.  I don't know how to see disk
> I/O.  I do know how to use top.  How do I measure disk I/O?  Any other
> thoughts?

Perhaps gstat(8) will help you get started:

# gstat -a

dT: 1.001s  w: 1.000s
 L(q)  ops/s    r/s   kBps   ms/r    w/s   kBps   ms/w   %busy Name
    4    176    114  10261   14.9     62    607   25.4   96.8| ar0
    4    177    115  10389   17.8     62    607   26.5  100.0| ar0.eli
    1     34     34    527   30.8      0      0    0.0   99.1| ar0.elie
    2     66      4     16   20.5     62    607   26.6   98.0| ar0.elif
    1     77     77   9845   12.1      0      0    0.0   93.0| ar0.elig

...or on ZFS:

# zpool iostat 1

               capacity     operations    bandwidth
pool         used  avail   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
storage     1.39T   440G      0    771      0  96.4M
storage     1.39T   440G      0  1.05K  4.42K   126M

Steve



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