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Server sizing

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Server sizing - 17.Oct.2006 7:58:47 AM   
ACL

 

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I want to consolidate a load of users on to a single server and I also want to make it capable of supporting up to 4000 'heavy' users. I'm aware that MS recommend 1 processor per 500 users but I'm also aware that they themselves have over 4000 users on a four way box. So my question is, is there any value in confguring an 8 way box for 4000 users?

Secondly, can a single dual core processor be considered the equivalent of two normal processors as far as Exchange is concerned i.e. is the maximum number of dual core processors Exchange can utilise 4 or 8?

Thirdly, Exchange can only use 4GB of memory so is that the maximum size you should make the box or is it worth configuring it with 6GB, the extra 2GB being used by the OS etc.?

Thank you
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RE: Server sizing - 17.Oct.2006 12:34:04 PM   
jchong

 

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Processory is usually not the bottleneck within Exchange, it's your I\O and memory. 4000 heavy users is stretching your resources. By heavy how are you determining this? What's the MB size that you wish to allocate and what's the IOPs per user you're working with? In additional, you need to size for any other services, such as indexing, Blackberries, which increase your IOPs per user by over 3 times, any users running desktop search engines etc. These are real bottlenecks to your disk IO. As far as using 6GB, I'm not exactly sure if the OS and overall server will benefit from that two GBs.

http://www.msexchange.org/tutorials/Art-Science-Sizing-Exchange2003-Part1.html

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RE: Server sizing - 17.Oct.2006 2:27:06 PM   
ACL

 

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Thanks for the reply James, unfortunately we don't have any baseline data for user mail profiles hence my desire to give the server maximum usable beef! Do you now anything about the dual core vs single processor issue?

I'm interested to hear you say that 4,000 users is stretching resources, surely there are plenty of Exchange servers out there with more users than this? Anyone care to verify or disagree with that generalisation?

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RE: Server sizing - 17.Oct.2006 3:20:13 PM   
a.grogan

 

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Hiya,

In terms of your memory sizing I would recommend about 4GB - any more really is a waste and you will have to add the /PAE switch to the boot.ini to take advantage of the addition RAM for the OS and it is recommended not to use /PAE with Exchange.

In terms of user sizing, I have a couple of Exchange clusters (active/passive) which have about 2200 and 3500 users per box (or virtual server) and the performance is pretty good.

In terms of your question about Dual cores, not really tried this - but I thought that although they do add a good performance hit unless the software is specifically designed to take advantage of the processing features - however, if you were to pick up a couple of DC Xeons then you are looking at a pretty spritely box.

In terms of disk, I use FC to shared storage, which seems to cope quite well, although I limit the size of a users mailbox the servers are always pretty busy - about 47,000 mail items per day, plus we make very heavy use of OWA and Windows mobile devices.

I find HP DL 380's very good options for Exchange (using SAN storage).

Hope this helps,

A

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RE: Server sizing - 18.Oct.2006 4:40:59 AM   
neilho

 

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Well, if you have existing users and servers then you will have some baseline data - you just have to go and get it. 

I know of Exchange servers with 4000-5000 users on them, sure.  It works.  But as James said, the key design decision surrounds the disk subsystem which is typically the bottleneck in any Exchange design.  If you don't design this properly, your 4000 users could easily overload the disk subsystem and performance will be crap.  And as others have said, there is simply no point in putting more than 4GB into an Exchange server - it won't be used.

Do yourself a favour and determine the IOPS profiles of your users at the moment.  You can use theoretical data if you desire, but the best thing to do is to work out the peak IOPS at the worst time of the week (Monday 9-11am for example) and then add 20% extra, etc.  It's all covered in the Exchange 2003 storage sizing document available from MS downloads, as is the CPU megacycles stuff.

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Neil Hobson
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