RE: BE disk config

  • From: "Mulnick, Al" <Al.Mulnick@xxxxxxxxxx>
  • To: "'[ExchangeList]'" <exchangelist@xxxxxxxxxxxxx>
  • Date: Wed, 15 Sep 2004 10:31:37 -0400

Unfortunately, that configuration is based on too little information for
sizing.  For example, what kind of user profile are we dealing with?  Are
they all pop users?  Are they all IMAP users?  Are they all MAPI users? How
much mail is being dealt with and how large is the average message?  

Why is this all important?  Because in order to size a disk subsystem to
work, you need to distill your user performance information down to a number
that represents the average user IOPS required.  Something like 1 IOPS per
user is required to sustain the performance expected during normal operating
times. That allows you to figure out how many spindles of what speed you
need to support your implementation.  


Obviously, IMAP, OWA and POP clients require different IOPS characteristics
than a MAPI client does due to the differing nature of their protocols.
15000 user density on a mailbox server is enough to want to thoroughly test
this scenario IMHO.  

Since all spindles are not created equal, you have to try to estimate the
IOPS capability of each.  For example, a 10K spindle is often able to
perform in the range of 90-120 IOPS depending on fragmentation, I/O
characteristics etc. A 15K drive is often able to perform at 140 - 160 IOPS
etc.  Size matters, since the more data you put on a spindle, the more
likely you are to go after that data and the more likely that spindle is to
be busy.  I.E. disk contention.  

Since you have to worry about 4 types of I/O, the usual recommendation is to
split the I/O types across different spindle sets.  In Greg's suggestion,
you see he put logs on a separate set of spindles and that's because log
files tend to have sequential write characteristics.  One block after
another gets written with lower read requests made to those spindles.

The SMTP characteristics tends to be a heavy write with some read.
Something like 80/20 w/r characteristics would not be uncommon.  That's
because the SMTP service will spool the incoming message to disk before
acting on it. When it does, it then needs to read it and move it to it's
queues or delivery.

Database drives tend to be random r/w in nature.  This gives SAN vendors
fits because they tend to want to size based on space, but random I/O is
cache-unfriendly in nature.  That means you need the spindles and there
isn't much magic that will help.  If you put Exchange on a SAN you're likely
to use the same number of spindle else spread it so far across your
spindles, that you have 128 disk sets in your volumes.  The only problem
there is that there are limits to what the underlying OS will deal with, so
you have to be careful to present in a way that you don't affect the OS
ability to address the devices.  Not difficult, just has to be contended
with.

Database drives tend to have a 3:1 r/w characteristic.  The problem with
RAID 5 in this situation is twofold: RAID 5 typically gives diminishing
returns after about 7 spindles due to the nature of RAID 5.  Adding a mirror
only gives you the ability to withstand the loss and some of the controllers
will also allow you smartly write the I/O from either spindle in the mirror
set resulting in better performance.  It still can be a 4x cost for write
operations on RAID 5 vs. RAID 0.  RAID 1 is often recommended because it
gives decent protection (tolerance of phys failures) while not sacrificing
performance.

Also, sizing the space: the typical recommendation is to use Greg's formula
+ multiplying it by 1.6 as a factor for other processes such as deleted
items retention.  

If you want to see more about sizing (and there is plenty more data
available) check out the whitepapers from Microsoft, HP, and EMC.  The 2003
stuff is pretty good at articulating the information.

If it helps, let us know the usage characteristics and we'll see if we can
help further.

HTH,

-Al
 


 

-----Original Message-----
From: Tim Sutton [mailto:t.sutton@xxxxxxxxxx] 
Sent: Wednesday, September 15, 2004 7:30 AM
To: [ExchangeList]
Subject: [exchangelist] RE: BE disk config

http://www.MSExchange.org/

I'd go with Greg's layout personally. Does he get a little gold star for it?
:)

The only other problem I can see is that you've got a lot of people all
dependant on one server, so if it falls / fails you could be in trouble.
Speaking from personal experience over the last few weeks having a single
point of failure for any critical (or even just mildly important) systems is
bad thing. Well, unless you like the stress and overtime ;)


Regards
Tim Sutton
IT Systems Manager

Troup Bywaters & Anders
Eastgate House
10 Eastgate
LEEDS LS2 7JL
Tel: 01132432241
Fax: 01132424024
E-mail: t.sutton@xxxxxxxxxx

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On Tue, 14 Sep 2004 13:54:34 -0500 (CDT), Monika Rabarison
<monika.k.rabarison@xxxxxxxxxxxxxxx> wrote:
> http://www.MSExchange.org/
> 
> Great! Thanks again,
> 
> Monika
> 
> On Tue, 14 Sep 2004, Lara, Greg wrote:
> 
> > http://www.MSExchange.org/
> > 
> > I'd agree with the hot spare idea as well. To figure your quota, 
> > simply
> 
> 
> > multiply the mailbox size by the number of users. If it exceeds your

> > available disk space, lower the quota. Leave yourself a 15-20% 
> > margin of error to be safe. 15000 mailboxes at 50 megabytes each 
> > equals 750 gigabytes, which is more than you'll have available even 
> > if you allocate all 8 72 gig drives to your RAID 5.
> >
> > It sounds like you're doing this for a school. I'd recommend a 
> > relatively low mailbox size, which forces people to keep their house

> > clean. 15000 mailboxes at 25 megs requires 300 gigs, which would be 
> > within your comfort level.
> >
> > Greg Lara
> >
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> >
> > -----Original Message-----
> > From: Monika Rabarison [mailto:monika.k.rabarison@xxxxxxxxxxxxxxx]
> > Sent: Tuesday, September 14, 2004 1:10 PM
> > To: [ExchangeList]
> > Subject: [exchangelist] RE: BE disk config
> >
> > http://www.MSExchange.org/
> >
> >
> > Shawn,
> >
> > The hot spare idea is a good one.
> >
> > Thanks  a  lot,
> >
> > Monika
> >
> > On Tue, 14 Sep 2004, Shawn Moua wrote:
> >
> > > http://www.MSExchange.org/
> > >
> > > I would vote for Greg's setup as well.  However, you may want to 
> > > leave a 72GB drive as a hot spare (assuming your system is
capable).
> > >
> > > Thanks,
> > > Shawn.
> > >
> > > -----Original Message-----
> > > From: Lara, Greg [mailto:GLara@xxxxxxx]
> > > Sent: Tuesday, September 14, 2004 9:42 AM
> > > To: [ExchangeList]
> > > Subject: [exchangelist] RE: BE disk config
> > >
> > > http://www.MSExchange.org/
> > >
> > > This sounds like a test question. Here's how I'd do it:
> > >
> > > "C" drive = 2 x 18 mirrored
> > > "D" drive = 2 x 36 mirrored
> > > "E" drive = 8 x 72 RAID 5 (or)
> > > "E" drive = 4 x 72 RAID 5 x 2 (RAID 5+1, that is mirrored RAID 5
> > > drives)
> > >
> > > The last option is the most secure, and costly, cutting your 
> > > possible database storage in half, and is probably a little over 
> > > the top for your needs.
> > >
> > > Install your system and boot files on C, Exchange logs on D, 
> > > private and public databases on E. Drive lettering for D and E 
> > > could be interchangeable.
> > >
> > > Greg Lara
> > >
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> > >
> > > -----Original Message-----
> > > From: Monika Rabarison [mailto:monika.k.rabarison@xxxxxxxxxxxxxxx]
> > > Sent: Tuesday, September 14, 2004 12:19 PM
> > > To: [ExchangeList]
> > > Subject: [exchangelist] BE disk config
> > >
> > > http://www.MSExchange.org/
> > >
> > >
> > > Hi all,
> > >
> > > I will have 15000 users and one BE server.
> > > What would be the best configuration for the
> > > (8 x 72 GB, 2 x 36 GB, 2 x 18 GB) disks on the BE?
> > >
> > > Thanks,
> > >
> > > Monika
> > >
> > >
> > >
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> > Monika Rabarison
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