Single Instance Storage with Exchange 2007


We have a sister company that is moving from Exchange 2003 to 2007 SP1. They will have 5000 users spread over 50 databases -i.e. 100 users/database.

We need to work out which users will be on which database. We could:

i) Allocate DB's by department to utilise Single Instance Storage (SIS)
ii) Allocate users randomly to each DB (e.g. by first letter of name)

There is a good article here on SIS:

What confuses me is that is states:

"SIS has also diminished in importance because of the way storage hardware has evolved. Over the past 10 years, the capacity of disk drives has risen sharply, but IO performance has remained flat, leaving most Exchange customers constrained by disk IO rather than disk space. In 1996, a typical disk was 10GB in size, and delivered about 100 IOPS; or about 10 IOPS/GB. Today, a typical disk is 500 GB and delivers about 100 IOPS; or about 0.2 IOPS/GB. The IOPS per GB has dropped 50 fold. Single instancing is fundamentally about saving disk space at the expense of increased IOs. So, while trading IOs to save space was a good strategy 10 years ago, today a focus on IO reduction makes more sense."

Question 1: How can we focus on IO reduction?

The article also states:

"In Exchange 2007, attachments are single instanced, but message bodies are not.

This behavior does not apply to the move mailbox operation, so when you transition to Exchange 2007 from Exchange 2000 or Exchange 2003, single instance storage is maintained for both message bodies and attachments, as long as:

The mailboxes being moved belong to the same source database and the same destination database
You are using a "transition" approach rather than a "migration" approach for your upgrade"

Question 2: So basically, SIS changes in Exchange 2007 so that only attachments use SIS, not message bodies? But this wouldnt have much effect would it since message bodies tend to be quite small anyway?

Question3: We may look to increase mailbox quotas for certain departments to over 1GB this year (e.g. for people who send a lot of graphic attachments). I assume for cases such as this, placing them in the same store would make sense to take advantage of SIS?
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SIS is gone in Exchange 2010 so going forward I don't see any reason to continue to plan your database design based on it. If you are concerned about disk space on your new deployment throw as much as you can afford at it or make sure its extendable.

In reposonse to your questions: -
1. Exchange 2007 and further in 2010 has much better IO performance. In large installation I still agree with keeping your database files and logs on independant disk spindles and in very large setups you may also have individual databases on independant spindles but this is largely in the hands of SAN Administrators these days.

2. Yes it won't have much affect as the body is usually small

3. Again SIS is not really going to give you a lot in terms of IO but may save some disk space but when you go to Exchange 2010 its not available anymore anyway.

Dude, Where's My Single Instance?

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