Never store PST files on network shares!

by Shijaz Abdulla on 07.01.2008 at 10:27

Most administrators think the best way to back up user’s Outlook PST files is to store it on a network share and let Outlook connect to it from a file share or mapped drive. This way all PST files are on a central location and backup is easy. Sounds like a nice strategy, doesn’t it?

Don’t ever do it. Ever.

Why? Here are two good reasons:

1. This can cause your file server to hang!

Believe it or not, the way Outlook access the PST files is aggressive. Let’s take an example. Early in the morning, some user sends out an email to 500 employees in your company. Some of these 500 users may need to extend their PST file in order to accomodate the incoming email message. To extend a PST, an extra allocation on the disk has to be made via NTFS. During this process, the whole volume is locked out while free space is allocated and the Master File Table (MFT) is updated. While this is happening for one user, all I/O for the other 499 users is on hold. This includes other users’ PST files as well as ordinary file shares on the same volume!

Now imagine if each user had multiple PST files! The disks get overloaded and the server suffers from serious performance issues. The queues for writing data to disk build up. This ultimately amounts to a server hang or PagedPool memory depletion!

2. It’s not supported

In case you were thinking – NO, it isn’t supported by Microsoft for you to store PST files on network shares. This restriction is not new, and has been around since Microsoft Exchange 4.0. This means storing PST files on a network share is an unsupported configuration and you will not receive support from Microsoft. For details, see MSKB article 297019.

Storing PST files on the file server is a very common mistake that administrators make and I thought it would be helpful if I posted it here.
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