Re: Why 4 Procs
- From: "Mulnick, Al" <Al.Mulnick@xxxxxxxxxx>
- To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
- Date: Mon, 31 Jan 2005 16:52:03 -0500
IIRC, the challenge is with Exchange in a 32-bit environment. The problem
isn't necessarily Exchange, but that's where the challenge is.
To get an A/A cluster with Exchange without that particular issue (note,
this is possible in existing implementations, but not recommended) you would
need a 64-bit version of Exchange.
To expand, the problem is with memory space. If you have an A/A cluster,
and you fail over, you may not be able to have the available contiguous
memory needed to operate as expected. This usually shows up in scaled-up
implementations vs. smaller clusters. The smaller the user-density, the
less likely you'll see the issues associated. But then, why spend the money
in most cases for that small an implementation right?
Side note: A lot of work went into RSG's and disaster recovery making
availability much much easier in Exchange 2003. Leaps and bounds over
Exchange 2000 IMHO. You can make an environment highly available if you
don't need the existing data immediately but just the functionality. If you
start going through the planning for BC/DR, I've often found that only a
small handful of people in a given corporation need that kind of effort.
For example, the mail clerk rarely needs 5x9's of availability, while the
CEO might need it. Often, even the most demanding user doesn't need the
legacy data back immediately, but rather needs to be able to continue email
to remain productive. To achieve such a thing, I've seen folks deploy the
so-called "dial-tone [1]" availability scenario where in the case of
failure, they'll associate the user object with a new mail store almost
immediately, recover the data to an RSG and trickle back the data over the
next 3 days (or whatever it takes). Can be very effective. I have seen some
that require higher availability of data and functionality, and often
they'll get into more expensive WAN, storage, and clustering technologies to
achieve along with clustering. Price is not typically the biggest issue for
those types of problems.
MSCS is a high-availability solution and not a cost-saving or fault-tolerant
solution. Once you get past that, it starts to make a lot more sense when
and if to deploy it to solve your needs.
Cheers,
Al
[1] I hate that moniker; it doesn't do Exchange/Windows justice. I've
deployed standalone solutions that were more reliable than the company
phones in terms of service to the user. It's perspective and planning, but
it can be done as I'm sure many have done as well [2]
[2] Ever seen companies that tell their users that the phone system is down
in a particular city and used email to do it? <G>
-----Original Message-----
From: paul_lemonidis@xxxxxxxxxxx [mailto:paul_lemonidis@xxxxxxxxxxx]
Sent: Monday, January 31, 2005 3:58 PM
To: [ExchangeList]
Subject: [exchangelist] Re: Why 4 Procs
http://www.MSExchange.org/
Hi Al
Many thanks for the info. It would seem that clustering is a very expensive
option taken all round.
One last question if I may.You mention to avoid A/A two node clusters.
Would the same apply to 64 bit Windows? Would we need a 64 bit version of
Exchange to get any gain from the basic 64 bit Windows platform upgrade?
Many thanks in advance.
Regards,
Paul Lemonidis.
----- Original Message -----
From: "Mulnick, Al" <Al.Mulnick@xxxxxxxxxx>
To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
Sent: Monday, January 31, 2005 2:19 PM
Subject: [exchangelist] Re: Why 4 Procs
> http://www.MSExchange.org/
>
> A cluster is a high-availability solution more than a load-balancing
> solution. It tends to be more expensive (capital costs) than a
> stand-alone
> system, and offers the higher-availability in terms of hardware failure.
>
> For your efforts, you basically get an automated "computer restarter"
> should
> hardware fail.
>
> To achieve this, Microsoft recommends having at least one passive node in
> the cluster. For example, if you deploy a 4 node cluster, you should
> deploy
> A/A/A/P, if 8 way, there's some thoughts that you should have a 6x2
> cluster.
> All active nodes, brings the PM's thoughts to mind: "For the love of God,
> don't do A/A clustering with Exchange on 32-bit platforms!!" Why?
> Plenty
> of reasons, such as memory limitations (32-bit platform limitations etc).
> Suffice to say, they have good reason to recommend this configuration.
>
> Additional downtime and upgrades can be avoided with clusters, since as
> you
> mentioned, you would have the option of adding an upgraded node, evicting
> a
> node etc when upgrades are needed. A so-called "rolling upgrade" can be
> done resulting in little downtime. Of course, if that's what I wanted, I
> could just move mailboxes over to a new server with little impact as well.
> Depends on what you need to accomplish.
>
> From a diminishing returns perspective, this would mean instead of a
> single
> 4-way machine, you'd deploy 3 2-way machines and one of them would be
> "dark"
> at all times waiting for failure. 6 processors, with 4 of them active at
> any
> given moment.
>
> Given the added expense of hardware (you'll need particular hardware and
> storage to make this work) and the added expense of cluster aware software
> (third-party cluster-aware apps), plus the learning curve associated,
> disaster recovery differences, etc, I'd say that 4-way looks pretty cheap
> in
> this scenario.
>
> If you need geographical availability, it gets much more complex and
> expensive.
>
> Clustering in Microsoft technology is for high-availability, and also does
> some load-balancing (you have to load balance it yourself, it's not
> automated in MSCS vs. Web load-balancing with NLB type of balancing).
>
> My thoughts anyway.
>
> Al
>
>
>
> -----Original Message-----
> From: Paul_Lemonidis@xxxxxxxxxxx [mailto:Paul_Lemonidis@xxxxxxxxxxx]
> Sent: Friday, January 28, 2005 1:15 PM
> To: [ExchangeList]
> Subject: [exchangelist] Re: Why 4 Procs
>
> http://www.MSExchange.org/
>
> Hi all
>
> Considering the likely cost of a 4 way box (the law of diminishing returns
> sets in fast once you go beyond 2 processors on a single box from I can
> discern?) and the disk space that would be required would a cluster of two
> two way boxes not be more cost effective?
>
> A cluster has the advantage of spreading the load as well as redundancy.
> Also many changes can be made to a cluster installation with no minimal or
> no downtime to users. I am thinking primarily of hardware maintenance, O/S
> updates (such as new software installation, hotfixes, Windows updates and
> Service Packs etc.)
>
> I would be interested to know people's thoughts? Many thanks in advance.
>
> Regards,
>
> Paul Lemonidis.
>
> ----- Original Message -----
> From: "Mulnick, Al" <Al.Mulnick@xxxxxxxxxx>
> To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
> Sent: Friday, January 28, 2005 3:47 PM
> Subject: [exchangelist] Re: Why 4 Procs
>
>
>> http://www.MSExchange.org/
>>
>> Mike, you bring highlight a great point. For a small implementation, a
>> single proc, if you can find them in a server chassis is likely fine for
>> just Exchange deployments. 100 users would likely be fine on a laptop if
>> not for the power-save functions :)
>>
>> Each deployment will differ greatly. For example, some will have 100
>> users
>> per server and of that, the 80-10-10 rule will apply for usage as well as
>> the 75/25 concept. 10% of the users will reply, "email? I have email? I
>> didn't know" 10% will be taking 80% of the resource utilization and the
>> other 80% of the user density will use the server on a normal basis
>> similar
>> to the benchmark specs.
>>
>> After that, you'll have to consider that not everybody uses a server at
>> the
>> same instant, so you might expect that 75% of the users would be active
>> (consuming resources) at a given time while 25% are making the company
>> money
>> in other ways. 75% is likely high, but I like to include the incoming
>> traffic that occurs when they do nothing.
>>
>> On a 100 user machine, a single proc would be fine most likely. A PDA
>> might
>> be enough if not for the storage requirements. On a 1000 user machine
>> you're odds of seeing it more heavily utilized with larger db's is
>> higher.
>> On a 10000 user machine, your odds are even greater.
>>
>> There's another angle to consider. Are all your users MAPI users? Or
>> are
>> some of them using internet protocols? If mixed, your resource
>> requirements
>> change yet again. It all needs to be considered.
>>
>> So you highlight a great point about the sizing of Exchange servers: it
>> depends. (sounds like something a consultant might say, doesn't it?)
>>
>> I believe the original poster mentioned 7000 users across 2-4 machines
>> (or
>> was it 5000 users?). That would be a density of about 3500 - 1750 per
>> machine depending on the final design decision. At 3500 user density I
>> can
>> tell that in most cases you won't want a dual-proc machine. It might
>> work
>> if you have a light or highly geographically dispersed user population
>> consuming the services and no other apps that suck the life out of the
>> procs
>> (like AV solutions tend to do). If you go 1750 per server, you're much
>> closer to border line. You may want to deploy with a 2 proc solution and
>> if
>> that doesn't work, upgrade to 4 way machines if the needs show you
>> require
>> it.
>>
>> Keep in mind what happens if you take Exchange to a sustained proc over
>> 75%.
>> It doesn't behave as well as you'd like, and any hiccup will result in
>> even
>> longer recovery times. Is that important? I think so, because what's
>> the
>> point of having email if you can't use it for days at a time? It needs to
>> be
>> as reliable as the door systems else it may as well go away.
>>
>> DR/BC requirements play a part in the decision process, since you may at
>> some point want to use RSG's to put mail back for some bozo that lost it
>> and
>> has to have it.
>>
>> On a 100 user system, you can likely tell them they'll be without mail
>> for
>
>> a
>> little while while you do the restore and the processor takes their
>> resources. Maybe during the lunch hour? On a 3500 user system, you have
>> much more utilization around the clock in most cases.
>>
>> Al
>>
>>
>>
>> -----Original Message-----
>> From: A. M. Salim [mailto:msalim@xxxxxxxxxxxx]
>> Sent: Friday, January 28, 2005 9:33 AM
>> To: [ExchangeList]
>> Subject: [exchangelist] Re: Why 4 Procs
>>
>> http://www.MSExchange.org/
>>
>> Hi,
>>
>>> Bottom line: you get better performance when scaling Exchange with
>>> four processor machines. Fact. You may get acceptable performance on
>>> a two-way machine. If you're really a small shop and can find a
>>> single processor server class machine (I'm sure they're out there, but
>>> I don't see them as
>>> frequently) then you may do just fine with that. In fact, I run
>>> Exchange on a single processor because it's a test lab in a VS
>>> environment. VS 2005 only supports 1 processor for VM. Not a choice
>>> at this point no matter how much hardware is presented.
>>
>> In an earlier email I asked why even 2-proc let alone 4-proc and
>> suggested
>> that perhaps there may be a tendency to over-spec as a CYA measure. Let
>> me
>> give you some specifics. Of the Exchange servers we manage, two are
>> single
>> CPU servers running P4/2.4 GHz and 512MB of RAM. Each of these two
>> servers
>> has about 100 users on it, moderate traffic and mailbox sizes (limited to
>> 100MB or less in most cases).
>>
>> The servers perform just fine. I routinely monitor the following
>> performance specs: CPU load, memory percent use, response speed,
>> complaints
>> of slowness.
>>
>> Results:
>>
>> CPU load: hardly a blip (generally under 5% or 10% load at any time even
>> at
>> peak time of day.
>>
>> Memory: well below 512MB usage. generally around 200MB or less.
>>
>> Bandwisdth/Network traffic: low usage. Well below 5% ustilization.
>>
>> Response speed: zero speed complaints in last 12 months (compared to
>> other
>> mailservers we have particularly a Windows based iMail server).
>>
>> Hence my comment about over-spec'd servers. From the emails on this
>> topic,
>> the consensus seems to be that a minimum 2-proc server is necessary for
>> an
>> Exchange installation, and I just don't see that based on the data I
>> have.
>>
>> Best regards
>> Mike
>>
>>
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