Single large .pst versus multiple smaller .pst's

Posted on 2008-06-11
Last Modified: 2010-04-21

I've been doing some research on Outlook 2007 performance issues and I was wondering if I could get some opinions.  

I found the following KB which mentions .pst/.ost file sizes and a brief description of the performance you could expect from each size range.  

My question is, are there any performance benefits to having several smaller .pst files compared to a single larger .pst?

We have a group of users at our site who are required to store email and calendar appointments from years past which causes some of them to have larger .pst's.  Their systems aren't exactly power houses and are scraping by with Office 2007.  We have many other similar model systems around the site but the very poor performance we're seeing seems to be isolated to the individual group that must keep their records.  

Thanks in advance for any info you guys can provide =)!

Question by:deltacollegeoit
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Accepted Solution

David Lee earned 125 total points
ID: 21762391
Hi, deltacollegeoit.

Performance covers a lot of territory.  Which are you more interested in, their ability to locate and open a particular item, or the effect on the computer?  From a computer perspective I expect that having a number of small PSTs all open simultaneoulsy is more demanding on the system.  Each open PST probably consumes addtional system resources (e.g. file handles, buffers, additional entries in underlying Outlook objects, etc.).  There may also be additional latency issues as Outlook reads from different files.  A single large PST will consume one file handle, one buffer or set of buffers, and is represented in Outlook by a single object.  However, given its size it may be slower to read since Outlook may have to perform multiple reads to get to a given item, where with multiple files it might be able to read more data in at once and fetch the item from memory without requiring an additional read operation.  Disk operations are typically the slowest portion of the system.  Some of these issues depend on how the users use the PST files.  For example, they can eliminate some of the concerns about mutliple PSTs by only opening one when they need it and closing it again as soon as they're done.  Without knowing how Outlook works behind the scenes and no empirical benchmarks to look at all I can do is guess.  

From a user perspective the performance issue is going to be driven by how they use Outlook.  If they spend most of my time in a few folders, then having multiple PSTs makes more sense.  Open only the PST you need and you open one small file.  Searches and object enumerations will all be faster since there are fewer items to process.  That'll improve usage performance although it may not have any significant impact on computer performance.
LVL 97

Assisted Solution

war1 earned 125 total points
ID: 21763188
Hello deltacollegeoit,

In addition to what BlueDevilFan said, Outlook 2007 has midigated the slowness issue with large PST file with SP1, so make sure that is installed.

How large is large?  I suggest keeping PST file size to under 1 GB. Some experts advise .5 MB or less.  This is for Outlook 2007 or earlier versions of Outlook.  Outlook writes to PST file all the time, so larger file are prong to corruption.  

Hope this helps!

Author Comment

ID: 21764167
Thank you for your responses.  I'm still trying to gather facts at the moment but the question just popped in my head and I wondered if there was any validity to it.

By performance, I meant the effect on the system itself.  This group of users have had system slowdowns when they first launch Outlook 2007 on start up.  It takes +10 minutes for the system to become usable, though it tends to speed up later in the day.  

Oh, and reading back on my first post, I forgot to add the KB article I had found.

And yes, they all currently have SP1 installed.

I'm not sure on the exact sizes but I'm sure they're above 1GB...which could still be underestimated considering their day-to-day duties and the duration that most have been here.

I'll be meeting with a couple of the individuals and I was hoping to try breaking down some of the largest .pst's into smaller segments but if what BlueDevilFan's theory is correctly, that might not be helpful.  

Author Closing Comment

ID: 31466237
Thank you both.  I'll be meeting with my customers but it won't be for a little bit longer.  I'll start playing with the .pst's and see what I can come up with.  I don't recall if I've tried flat out temporarily removing their .pst's or not yet so that will be the first thing I do.  If that improves things, I'll pick it up from there.

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