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exchange 2013 | outlook online mode

cmatchett
cmatchett asked
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When running outlook in online mode, is it more memory intensive or CPU intensive on the exchange server?
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Will SzymkowskiSenior Solution Architect
Most Valuable Expert 2015
Top Expert 2015

Commented:

When running outlook in online mode, is it more memory intensive or CPU intensive on the exchange server?

That is correct. When you are using Online mode you are actually using more resources on your client machine and also the Exchange server. This is because your client has a direct connection (over the network) to the Exchange server.

This is why Outlook has cached mode enabled by default. In cached mode you are referencing your local cached copy (OST) file first before reference the Exchange server. This is the same a the GAL. When you are using cached mode you are not actually referencing the GAL but the Offline Address Book instead.

When using cached mode you will experience some delays in regards to GAL updates ect because you have to wait for the OAB to populate the new items when it updates (default is once a day).

Depending on the size of your mailbox is also important because if you have a very large mailbox (20+GB) you have a higher chance of OST corruption. So make sure that this is controlled using quotas.

Will.

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Commented:
Is it more CPU or memory though?  I have read that exchange caches the requests from outlook in online mode in memory, meaning that it's more memory intensive than CPU?
Senior Solution Architect
Most Valuable Expert 2015
Top Expert 2015
Commented:
When a client connects using Online mode it makes a direct connection to the Information store, this does ultimately does take up memory but Store.exe is designed to grab as much memory it "thinks" it needs to perform, without compromising server performance. It is also CPU intensive as well when doing searches and other processes from IIS etc.

I have not been able to find any references (TechNet) on what is affected more "CPU or RAM" when using Outlook online mode. However you need to take in to consideration that the size of the mailbox does have a contributing factor and also it will affect both CPU and RAM to some degree.

I guess if you wanted a more accurate reading you can use performance monitoring and create data collector sets for Memory and CPU, to collect info from users connected. As stated this depends on who is actually using online mode. A user with a 1GB mailbox will have less affect on the server than someone with a 25GB mailbox.

Based on how Exchange is designed to chew up memory to increase performance it make most sense to me that RAM would be utilized more than CPU, but CPU would still be affected.

Will.