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Why is Exchange Server store size important in the case of a disaster recovery situation?

A good proportion of the customers I speak with need their data back as soon as possible when disaster strikes, but there are many factors that actually affect the speed of a restore. Depending on the setup of the Exchange environment, a recovery can become extremely complex and time-consuming. In this penultimate post of our Exchange series, we’ll understand the role that Exchange Server store sizes play when disaster strikes.

Why is Exchange Server store size important in the case of a disaster recovery situation?

When looking at an Exchange Server store size, it is first important to note what exactly this includes. In “Determining the True Amount of Space in an Exchange Database”, which includes some tips on how to understand and clean up your database, 90% of the of the space used in the database is attributed to pages at the database root, messages tables, folders tables, and attachments tables; they normally represent the greatest amount of allocated space (white space) in the database. The remaining 10% comes from the additional information that Microsoft Exchange requires to function, e.g. search folders, indexes, and system tables.

folderSo, how can this have a reaching effect on a disaster recovery situation? Well, when we consider the previous question on mailbox quotas, we can see that available space and the proper management of this space is an important factor when trying to retrieve a recent backup in the event of data loss. The key question in managing this space is: how much is really available to you?

The next important consideration when looking at store size in disaster recovery is the potential recovery time, i.e. how long will it take to get your business back online in the event of a data loss or disaster situation. Most customers who come to us asking for help usually want their data recovered “yesterday”. However, in realistic terms, the time taken to recover a large store from a backup can vary greatly depending on how they are managed. Some key questions to ask when looking at the Exchange Server store size in a system are:

1.      How long do preliminary installs take?

In a disaster recovery scenario where there is a complete system outage, the time taken to reinstall the operating system, the Exchange Server and your service packs should not be underestimated. Keep in mind these are all required steps that need to be taken before the Exchange Server databases can even start to be restored.

2.      What is your media transfer rate?

This can affect the speed at which the store is restored and can be very slow if the correct technology is not applied in cases where the store size is very large. Similar to the mailbox quota, realistic and controlled amounts need to be applied, depending on the individual capabilities and needs of an organisation.

3.      What does the distribution of data look like over the Exchange Server stores?

It goes without saying that smaller restores are quicker and easier to implement than larger restores. Therefore, it is usually recommended to distribute mailboxes over multiple storage groups so that, in the event of a disaster recovery scenario, there is reduced risk of data loss, less downtime and fewer users are affected by it.

In my next (and last) post of our Exchange series I’ll be answering a common question around Public Folder database restores and some techniques you can use to granularly restore deleted items.

As always, feel free to leave your comments or questions in the section below. See you then!

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