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Why not use OST without cache mode?

Posted on 2008-06-16
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Last Modified: 2012-06-27
I have seen many postings here about Outlook 2003 cache mode and Exchange 2003. However, one thing is still not clear. Why not use OST and disable cache mode? It seems that in cache mode, Outlook is always trying to adjust on how and when to connect to Exchange 2003. With cache mode, we have had users complain about slow response even when they are on LAN.
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Question by:nkulsh
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13 Comments
 
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Expert Comment

by:kieran_b
ID: 21798184
OST is cached mode - you can't separate the two.

Cached mode refers to your local outlook client keeping a cache or copy of emails that will be available offline - it keeps these files in an OST.

To use an OST without cached mode would mean you have an OST with nothing in it - to have cached mode without an OST means you have an offline cache of nothing.

Why not just use online mode?
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Author Comment

by:nkulsh
ID: 21798225
I think you are wrong. I have an OST file on my Outlook 2003 right now and its size is about 300 MB and growing but I have cache mode disabled.
You will have an OST file for sure if you enable cache mode but you can have OST file without cache mode as it was in previous versions of Outlook.
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Expert Comment

by:kieran_b
ID: 21798249
That is a PST file - completely different.

The downsides to PST files are many, including, but not limited to;

No network support for PST files
No multiple user access to PST files
No centralised storage (and therefore backup) of PST files
Redundancy of OWA and RPC/HTTP as there is nothing in the server mailbox.

If you want to use PST files, you are wasting your Exchange server license.
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Author Comment

by:nkulsh
ID: 21798291
I very well know all the negatives of PST files, as constantly hammered in by MVPs like Ed Crowley in Exchange groups.
I am talking about OST file which can be created from Advanced tab of More Settings window, independent of cache mode. Try iit...
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Expert Comment

by:kieran_b
ID: 21798308
That is cached mode
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Author Comment

by:nkulsh
ID: 21798336
Wrong!
This could be done even in Outlook 2002 and there was not cache mode then. Also it does not have verious mechanism in place that are part of cache mode -- and which sometines cause performance issues.
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Expert Comment

by:kieran_b
ID: 21798608
Offline folders is the old name for cached mode.

I wish you the best of luck, but have little interest in volunteering any more of my time to help you
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Expert Comment

by:esenger
ID: 21799383
Unfortunately, the OST file is for offline or cached storage not for primary usage.  The Offline File Folder settings you mention are designed for mobile users who connect and disconnect from the network using a dial-up connection (almost unheard of in these days, but we used to use this more frequently in ancient times).  The OST file uses the same format as the PST with all of the same drawbacks.

Unless your network has frequent outages, I wouldn't recommend using cached mode.  It's frustrating that Microsoft sets it as the default.  Not only is there a delay sometimes in message receiving or sending (as the OST file syncs with Exchange), but sending mail uses the offline/cached address book as the default.  If your GAL is frequently updated, this causes problems when sending to new users.
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Author Comment

by:nkulsh
ID: 21799508
There is one big difference between OST and PST files. OST is a copy of what is kept on Exchange server while PST -- configured as the destination of new email -- moves the mail away from Exchange database, and thus a very unwise choice in most cases.

Due to performance problem with cached mode, we have disabled it in our network with a GPO. However, I do want a few important users to have OST files in case Exchange server crashes. They will have all their emails in such a event if they stay offline.

My original question asked about the drawbacks of not using cached mode? You seem to say it is good riddence, right?
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Expert Comment

by:CrazyStand
ID: 21803495
The downside to Online mode is that it places a larger strain on your Exchange server by using more resources per user connection (memory, CPU, etc)
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Author Comment

by:nkulsh
ID: 21807057
"Online mode"? Do you mean "cache mode"? Are you also saying that cache mode is not so great?
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Accepted Solution

by:
CrazyStand earned 125 total points
ID: 21807424
You asked what are the drawbacks of  -not- using cached mod are.  Not using cached mode means that you will be using Online mode.  Online mode requires more Exchange server resources as clients will utilize the server more.  Clients will directly access the server to do things such as searches or view new mail as opposed to downloading the message and viewing it out of the ost cache.

Personally I like cached mode.  I find that it is more responsive and resilient to minor network blips.  I agree with esenger in that the cached mode address book only updating once a day is annoying.

There are drawbacks to either way.  You already said you disabled cached mode due to performance issues in your environment so cached mode doesn't sound like much of an option anyway.
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Assisted Solution

by:esenger
esenger earned 125 total points
ID: 21807680
Since your primary goal is to protect certain users against an Exchange server outage and you are controlling cached mode using Group Policy, what I would suggest would be to turn off cached mode unless you see instability in the Exchange server.  I've been through several Exchange outages, and every time there is ample warning.  When you see problems occurring in the logs, you could then enable cached mode for those critical users.  
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