The Good, Bad, & Ugly of Email Archiving

Quite often, I get to the question of "so how do you archive your email?" While responses differ, at least once a week, the answer is..."Oh, we request users archive their email using Outlook Personal Storage (or, .PST files)."

Woah, time-out!

The good news is that this problematic situation is very common and well-known. Bad news being that PST files on LAN/WAN is totally unsupported by Microsoft (see: http://support.microsoft.com/kb/297019).

The next question comes from the techies in the crowd: "How come? What's the big deal?" My explanation goes like this:

Pretend you work at a 1,000-person company. Now, let's say that half of them use PST files as their email archival with an average size of 1 gig. Now consider what happens when all 500 PST users launch Outlook when they arrive to work in the morning.

500 x 1 = 500 GB of disk & network I/O to process simultaneously. All sorts of queuing issues -- the Windows Server Service allocates various worker threads from the kernel's Non-Paged Pool (NPP).

Then, I/O requests are sent to the disk subsystem (let's say it's a NetApp FAS system). What if the disk subsystem does not respond in time? All incoming I/O requests are queued as "work items". Since there are finite memory resources, NPP will (eventually) run out, log a System Event ID 2019, and hang the server.

You can actually view this steady depletion with perfmon with the "Available Work Items" counter. If you're AWI is close to 0 (zero), clients may be dangerously close to not being able to access their files.

Sure, you could tweak to mitigate some of these negative issues, but as you scale upwards, the server itself may not be handle to workload and your house of cards falls down.

This problem could be solved in different ways: You could...

- use an Offline Storage file (or .OST),
- deploy a Microsoft Terminal Services farm,
- implement a third-party email archiving app,

...and back it all up with NetApp FAS systems. Remember this one key point:

PSTs are not an enterprise storage solution !!