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Any (dis)advantages in using more than one mailbox database?

jogarnes asked
Medium Priority
Last Modified: 2012-05-06
Hi. Is there any (dis)advantages in using more than one mailbox database? Like if you maybe have a hosting solution or just want to put a group of people in one place...

If you use one database (store) you will have a bigger problem if that fails instead of one of the stores. Will the server consume more CPU, harddisk access, etc?

Any pointers would be great!
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The actual recommended configuration from MS is one DB per Storage Group. So, if you were to add another DB, it should also be in a new storage group. Microsoft also recommends (as a best practice) to not have Mailboxes Databases larger than 100GB. Also - DB files and Log Files should ALWAYS be on seperate physcial disk arrays.

All of these recommendations stem from Disaster Recovery (DR) Best Practices.

If each db is in its own storage group, then each db will also have a dedicated log file.
This also allows unique StorageGroup settings and DB Settings, and isolated maintenance. This is ideal for hosting.
The 100GB limit is ra recommendation based upon the time to restore/recover a database.
The store process  will grow to accomodate all available memory resources regardless of the number of databases - so Ram impact would be difficult to judge. There is a Base hit in performance per DB, but it is negligable if the box meets the suggested sizing requirements.

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The only time you get a performance impact with multiple databases is if the storage was poorly designed in the first place and was already creaking. The extra set of transaction logs and databases can push things over the edge. Rather than dealing with two sets of writes, the server could be dealing with four.

However as with many things with Exchange, the most common reason is a design decision, as already outlined, it is for data recovery purposes. It can also allow you to have different settings for each mailbox store.

Should something happen to the database there is less to restore if it is split up, plus you can prioritise the data recovery if the database has been laid out correctly.

I guess there is no wrong or right answer to this question, it is something that you need to look at and decide if it is right for your company. It does no harm to try and use multiple databases and if you find that it causes you problems then you can always move the data back. You don't lose anything.

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