Re: % Disk Time

From: Andrew J. Kelly (sqlmvpnooospam_at_shadhawk.com)
Date: 08/06/04 

Date: Fri, 6 Aug 2004 15:48:22 -0400

That counter is pretty much useless in my opinion. I have seen this vary
greatly with the different types of hardware used. It's better to use the
Avg and current Disk queues instead. They give a much better view of how
your drives are able to handle the load. By the way are these drives
Logical or Physical? 

-- 
Andrew J. Kelly  SQL MVP
"Mike" <anonymous@discussions.microsoft.com> wrote in message
news:192c01c47bea$40735340$a601280a@phx.gbl...
>
> I have separate drives each SQL Server database:
> database file (E:)
> database transaction log (K:)
> tempdb (M:)
> database system files (F:)
>
> My database % Disk Time: (Average = 2541, STDEV = 4316,
> Maximum = 86770)
>
> How is the % Disk Time measured?
>
> The % Disk Time high at 55%?
>
> Thanks,
>
> ___________________________________________________________
>
> Brian
> First of all i have said 'probably'
> Secondly if you have this counter higher than 55% for
> continuous periods
> (let me say 15 min)then your SQL Server
>
>
> may be experiencing an I/O bottleneck.
> "Brian Moran" <brian@solidqualitylearning.com> wrote in
> message
> news:%23r7TWIieEHA.2848@TK2MSFTNGP10.phx.gbl...
> > I don't tend to agree with that advice.
> >
> > On it's own
> > <<
> > '%Disk Time
> > >>
> >
> > Is not a very reliable indicator of an IO bottleneck.
> You could easily
> have
> > a bottleneck if this counter is much lower than 55%. You
> might NOT have a
> > bottleneck if this counter is 55% or higher.
> >
> > There are many, many more counters which you should take
> a look. You need
> to
> > take a look at queue lenght, wait times for disk
> transfers, time it takes
> > per read and write.  In addition, there are a host of
> other counters
> > specific to your SAN that you should take a look at.
> >
> >
> > Unfortunately, I'm running a bit late right now and I
> don't have time to
> > write a long message. Tom Davidson from MS has a nice
> article in SQL
> Server
> > Magazine that dicusses some of these counters. I believe
> it might also be
> on
> > MSDN. It shouldn't be too hard to track down if you
> search by his name on
> > each site.
> > -- 
> >
> > Brian Moran
> >
> > "Uri Dimant" <urid@iscar.co.il> wrote in message
> > news:u1rJ0yheEHA.3520@TK2MSFTNGP10.phx.gbl...
> > > Mike
> > > This counter measured how busy a physical array is. In
> general it should
> > be
> > > less 55% otherwise you probably jave IO bottleneck.
> > >
> > >
> > >
> I have a Windows 2000 Advanced Server with SQL Server 2000
> Enterprise Edition on a SAN.  What units are the %Disk
> Time measured in from Perfmon?
>
> Is the (% Disk Time E) = (Disk Time E) / (Total % Disk
> Time) ?
>
> Please help me with these questions.
>
> Thanks,
>
> Mike
>

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