Exchange Migration Store Question


I've been testing a migration to move email from an Exchange 2007 to Exchange 2010 server.  It's about 60 users or so and am going to just export and import as it's a brand new domain.

I've tested it and mapped X500 addresses so there are no bounces.  As well as turn on circular logging to cut down on transaction logs during this phase.  What I am wondering is should I expect an information store of around the same size on the new server from the old?

It is around 100 GB.  Not sure if others have experience with this as I've not had to do this before.
Who is Participating?
Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
There is no SIS in Exchange 2010 .... exclude the SIS and i guess it should be around 125GB or almost the same size that of the PST's for all users.

I guess best would be to create multiple Database on the new server to keep the database size around 50Gb for good administartion ... Backup and Restore would be quicker as well.

- Rancy
Manpreet SIngh KhatraSolutions Architect, Project LeadCommented:
What i meant was the SIS would be broken if any on the old database while you export the data from users mailbox to PST ..... so once you have the data in PST you can check with the collective size and thats what is the total size and if you have Exchange 2010 SSTD you can have 5 Database ....

- Rancy
Normally when you export - email pointers break *Single instance Storage*, hence each message which earlier had say five pointers being linked to five mailboxes, after export will break into five messages. Hence, 1Meg email will become 5 meg file post export.

As per calculation normally your size of entire PST should be around 30-40% more than your actual database size (Actual = Total DB Size - white space)

How are you doing the migration? Your mention of mapping the X.500 addresses across suggests this is a cross-forest move using remove mailbox move requests from Exchange 2010? (Since X.500 mapping isn't necessary if you are moving within the same Exchange organisation!)

As the others have mentioned, Exchange 2010 does away with Single Instance Storage (SIS) completely. There is no such thing in Exchange 2010. This was a conscious decision by the product group to reduce disk IOPS, drive up performance on cheaper and lower specified hardware, which was ultimately intended to reduce the TCO of an Exchange deployment to an organisation. Exchange 2007 only had SIS for attachments (not the actual message text), so it was already on its way out with that release. The others have quoted valid figures for an average case, but you are definitely going to lose SIS regardless of whether you export to PST or not. If you deal with a lot of bulky attachments transmitted to lots of users within your org, then losing SIS on those and storing each attachment separately could hit greater than you expect. There are no methods I am aware of which allow you to predict this before you move the mailboxes and analyse the effect.

You should also check the whitespace present in the database. If you have an inordinate amount of whitespace, then you can expect that to be a net decrease in the size of the new database. Whitespace is composed of database pages allocated on disk but which contain zero information whatsoever, simply left over from old data which was purged from the database but the space was never released by Exchange from the EDB file (doing so is an unnecessary performance hit). Since this contains absolutely no data, none of the whitespace will be moved across. You won't have a lot of whitespace unless you have recently deleted a lot of data from user mailboxes or deleted a lot of mailboxes themselves, and then allowed time for that deletion to make its way to the underlying Exchange database engine.

mmichaAuthor Commented:
Thanks all for the input!
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