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We're running Small Business Server 2003 here. I was reviewing our backup procedures lately and noticed in the ntbackup logs that the differential backups of Exchange were failing with the error:

(SERVERNAME)\Microsoft Information Store\First Storage Group is not a valid drive, or you do not have access.

A quick search of google found this MS KB article: http://support.microsoft.com/kb/555613 However, both of the suggested fixes don't to apply to our problem. First solution is to make sure the backup media is formatted and has adequate space. Well, our backup target is a 1 TB external hard drive with about 600 gigs of free space. (A full backup of our Exchange DB is currently around 5 GB) The second suggested fix is to "perform a full backup before trying to do incremental". And again, that can't it because we are doing full backups twice a week.

There are no errors in the application log, just entries for ntbackup starting and ending. I've also tested doing an differential & incremental backup onto the server's internal drive, which unsurprising still did not work.

I could get around this problem by always doing a full backup of Exchange but I kind of like the idea of being space efficient with doing differential backups.

Anyone got any ideas?

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3 Answers

Wow, my googling skills failed me this time. I did some more searching and eventually found my answer:

Incremental and differential backups don't work on Exchange when circular logging is enabled. On top of that, SBS 2003 has circular logging turned on by default. Apparently, there were some newbie SBS admins that never did exchange backups, and their hard drives would eventually get full of Exchange logs. So the SBS team decided to ship exchange with circular logging turned on.

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I forgot to mention that I have since turned off circular logging and now the differential backups are running fine. –  voon Mar 22 '10 at 15:18
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SBS is best backed up using the built-in backup wizard. SBS does full backups only using the out-of-the-box tools. If you need to get more sophisticated, it's best to buy a third party solution such as Symantec Backup Exec.

As you already discovered, SBS uses 'circular logging' for exchange databases. This means that it maintains only a minimal transaction log and the log is recycled. Normally, the exchange transaction log is retained until a full backup is performed, then deleted. This doesn'r apply when circular logging is used because the same small transaction log file is re-used over and over. A differential backup would therefore have nothing to back up and doesn't make any sense when circular logging is enabled.

Backup exec has some useful additional capabilities over the exchange-aware version of NTBAckup, such as the ability to backup and restore down to individual mailboxes and messages. It may well be worth considering.

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I believe the Exchange store is a form of database (either JET or MS-SQL related). You can't do a "differential" of this file because if the exchange server is running, it isn't guaranteed to be consistent, and it might change at any moment (including halfway through your backup).

You need a specialized backup tool to handle exchange properly unless you shut exchange down during the backup. Even then, you'll want to do a "full" backup of the store.

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-1 This answer is a bit misleading. Exchange does require special backup software, but it ships with its own exchange-aware version of NTBackup (and that includes when installed as part of Small Business Server). NTBackup uses the Volume Shadow Copy Service (VSS) which ensures consistent backups oven for open files and databases such as Exchange mailbox stores. An exchange 'differential' backup is actually a transaction log backup and doesn't backup the main database file at all. When restoring, exchange will 'roll forward' the uncommitted transactions. –  Tim Long Mar 21 '10 at 17:29
    
Fair enough, I didn't know that. –  David Mackintosh Mar 22 '10 at 2:16
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