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When do I need another Exchange Server

Posted on 2015-02-24
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Last Modified: 2016-11-23
Hi Guys,

I look after several clients with on premise Exchange Servers. Most clients are relatively small but I have one that has grown quite considerably in the last 12 months and they now have 150 mailboxes on a single Exchange Server. The mailboxes have a combined size of 250GB and are spread over 5 databases.

Its a Exchange 2013 (SP1) Server and is running virtually (HyperV). The Physical host is a Dell Powerdge R710 with 6x 600GB 15k SAS disks in RAID 5.

The Exchange VM has 16GB of RAM and 8 CPU's allocated to it. The databases are stored physically on the RAID 5 disk set using two different virtual disks.

The issue Im having is the client is reporting Exchange Freezing a random times during the day. The Exchange Server was originally pretty quick but has slowed down as more users have been added to it. The client reports the freezing occurs multiple times every hours and lasts for 10secs+ each time.


My question is this - given the above setup, how many users should I be expecting to run comfortably off this Exchange 2013 Server?


At what point typically would you consider adding another Exchange Server? I haven't tried any performance tweaks (other than sprading the load overe several databases), its a stock install. I know its good to have a second Exchange Server for redundancy (so I will be probably adding a second one anyway) - but based purely on performance considerations, is there a magic number of mailboxes you can typically get working off a single Exchange 2013 Server?

I tried to use the Excel calculators provided by MS, but they seem to be suited more towards companies with bigger user bases.

The client is also not interested in Office 365 because they want to keep all their data in house.
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Question by:Barry Craig
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Scott Thomson earned 200 total points
ID: 40629670
Hi Barry Craig,

Unfortunately Exchange is not my special area of expertise. But i do have something to contribute on this matter for you.
Do you know if the clients are running live clients or cache mode on their outlooks?

with 150 mailboxes and all users plotting away you will definitely begin to see this kind of issue in live mode vs cache exchange.

I would suggest maybe to switch them to cache mode (better anyway really) and see if the issue resolves or slows down. Simply recreating their mail profile and setting to cache mode should do it easy enough. but remember their nk2 files. If you are interested i will post some more info just let me know. but it sounds like they are running in live mode and starting to hammer their network a little bit too much.
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by:Will Szymkowski
ID: 40629680
What version of Exchange are you running? If you are running Standard then you can only have 5 mailbox database per Exchange server holding the mailbox role. How big are each of your database currently? You said that in total you have 250GB of mail across all mailboxes. So I am guessing each of your mailboxes are around the 50GB?

If that is true then you do have a considerable amount of growth available. Theoretically you can have up to 16TB database, but this is not practical when it comes to backup and maintenance but having a 400-500GB database is completely acceptable.

Also if you plan to incorporate another Exchange Server this will be added licenses so I would leverage both DAG members 2/3 split so that you can get use out of both mailbox database servers. Also load balancing CAS as well with a hardware load balancer is preferred.

Check out performance sizing
Performance Sizing Cheat Sheet

Sizing Deployments

Will.
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by:rgorman
ID: 40629686
Your one server should be fine for the user base you have.  I agree with the above statement about switching to cached mode.  It will reduce quite a bit of load on the server.  Every time a user does a search of their mailbox in Online mode it puts a hurt on the Exchange server.  If enough people are searching all once then you could have performance issues like you are experiencing.  In cached mode the local Outlook client does the indexing and it just synchronizes the email which is much less demanding on the server.

You can turn caching on through a GPO if you want.  Just be careful when you do, if all the users log in at the same time after you enable it then they will all be downloading all their mail at the same time which could be quite slow.  You could filter the GPO to a group of users and slowly add groups of people until they are all done.

I am not sure what you are doing for backups on the Exchange server but I have seen some DPM implementations and other third party backup solutions that run quite frequently and those too could be hurting your server performance during the day when it is being used.  You may want to double check your maintenance schedule.

Other than that, adding a second server COULD help your load if you had the physical resources to add a second virtual Exchange.  If you have the spare resources though you can try and just bump up Exchange and see if that helps.
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by:Will Szymkowski
ID: 40629691
Not sure why the users would not be using cached mode as it is enabled by default.

Will.
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by:dlethe
ID: 40629694
It isn't the user count, or database size that tells you when you bust out.  It depends on how the users are using the system.  What is average cpu, memory, disk, and network utilization?   Find the bottleneck.    I'll tell you one thing, doing RAID5 is HORRIBLE for exchange.  You might  need nothing more than to add a pair of 15K RPM drives, configure as a RAID1, and move the O/S, swap, and scratch table space there.  If you're disk I/O bound this could very well give you a 2-5X improvement in overall system performance.

Note the 2 disks must be dedicated to the exchange VM, not shared among everything.  VMWARE is not efficient at disk I/O.
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by:Barry Craig
ID: 40629695
We are running Exchange 2013 Standard and the databases range from 20 to 90GB, they are split along logical organisational lines.

So if we are having performance issues, can you point me towards some literature which will help be debug why the server isn't performing well?

From what you are telling me, I assume a single Exchange 2013 Server should have no problem with running many more mailboxes than what this client currently has and if there is slowness I should be looking for hardware bottleneck?
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by:Barry Craig
ID: 40629700
The reason why Cached isnt turned on by default is because most of the users access Exchange via Remote Desktop Services. I might just have to add another volume to these RDS Servers and dump the OST files there ...

Just regarding the comment about RAID 5 not being good for Exchange, are there any best practice guides you can point me towards?

I am about to deploy a Dell MD3860' SAN for this client, so I will be able to reconfigure the disks how I like. Which RAID set do you recommend I configure for the Exchange OS Partition and which RAID Set should configure for the Data?
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by:Scott Thomson
Scott Thomson earned 200 total points
ID: 40629705
Hi Barry,

It's not necessarily the "size" of the database that could be the issue but the "amount" of users accessing the databses.
And at first guess i would not believe it to be so much of a bottleneck as much as a "constant hammering"

Even in raid 5 with multiple disks 150 people simultaneously accessing 2 - 3 emails in a row is probably too much for the disks to handle in 1 go. by the time it spins up and down to look at the live email of all these users the user will experience a "lag" of about 10 seconds or less while the disk scurries up and down to read the email. That is why the issue is not constant and the time might vary.

Placing in cache mode makes the mail download to the users hard disk and not be read directly from the server. This in turn allows them to browse their mail with ease without the server constantly spinning up and down to get their emails.

Ths is better from a hardware perspective in read/writes before a drive dies and better in speed because it uses no network traffic except for the original download of mail as it flows throughout the day
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by:Scott Thomson
ID: 40629713
By remote do you mean remote desktop? ie they dial into their work desktop machine?
Or via VPN?
Either way cached would still be better for the user
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by:Will Szymkowski
Will Szymkowski earned 200 total points
ID: 40629715
RAID1 is the best for performance for Exchange Database and Logs. the link for Sizing Deployments has the storage requirements and what is recommened in regrads to having it properly setup. I am assuming that your performance is being degraded because of how the virtual environment is configured (looking at 30,000 foot view, based on what you have said already).

Also with Exchange do you have hyper threading enable? Exchange performs better without hyper threading enabled and should be left disabled.

check the links i have provided for full details and also look at your vitrual environment setup i.e. resources/disk/cpu/ram etc.

Will.
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by:Lee W, MVP
Lee W, MVP earned 100 total points
ID: 40629753
To chime in, 150 users should be fine for most situations but the problems you're experiencing are very likely performance related.  You should start with Performance Monitor and examine your values.  Ideally, you should do this YEARLY to watch performance changes and know when you should upgrade or change things.  In your situation, I would create a performance log from another, more lightly used Exchange install and compare their values to this server.  Some things should be proportionate, but others won't - I'd start with looking up those values that are far above what they should be - I suspect your issue is disk based.

As for guidance on Exchange / Database performance, I would look for a controller that supports an SSD Cache and configure a RAID 10 for ideal performance - I've done some testing on Software RAID 5 vs. Single disks and the performance was about 33% of what a regular disk gets.

Some references for Performance monitoring:

https://technet.microsoft.com/en-us/library/dd335215%28v=exchg.141%29.aspx

https://technet.microsoft.com/en-us/magazine/dd560697.aspx

https://technet.microsoft.com/en-us/library/ff367896%28v=exchg.141%29.aspx

These may be written for older versions of exchange but concepts and often counters will still be the same and likely just as relevant.
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by:Scott Thomson
ID: 40629913
These other guys are much better with Exchange than myself but i would suggest starting with cache mode just because its the easiest to do and requires no investment or updating of systems. See if you get any improvement and then move on from there with the other experts suggestions if needed

Good luck ^_^
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by:Barry Craig
ID: 40629917
thanks.
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