Best way to move mailboxes off large mailbox store in Exchange 2007

I inherited a massive 450 gig mailbox store that houses the majority of our mailboxes in Exchange 2007. This store is apparently heavily fragmented, and it's not unusual for it to take a long time to process larger e-mails. It's also not unusual for a lot of e-mails sent and received to be over 20 megs in size.

That being said, I'm thinking that I really need to move these mailboxes to alternate storage groups to minimize this issue. However, given the large fragmentation and mailbox sizes (most are in the 5 - 10 GB range, some as high as 28 GB), it takes forever to move. I tried to move four 5 gig mailboxes over the long weekend, but had to cancel it after they ran for 48 hours and didn't finish.

With regard to the fragmentation, I've held off on running a defragment, since my understanding is that it would take many days to complete and would even further impact this database. Perhaps my logic here is incorrect?

So, this leads me to my question of what strategy should I take to address this issue while minimizing the impact to the staff actively using it? I've asked staff to start emptying their deleted items and archiving more to help reduce the mailbox size, but I'm wondering is perhaps restoring an old backup to another server and doing some sort of move and merge, or something along those lines is possible?

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AmitIT ArchitectCommented:
450GB database is not that big. Exchange server performance depends on server hardware, especially disk speed. Best approach here would be, as you already ask your staff members to reduce mailbox size or archive. once that task is completed, you can start moving the mailboxes to another DB, basically distribute it to other DB's. Also implement mailbox limit, 2GB would be enough. You can also move to Exchange 2010 or 2013, which support much larger mailboxes and databases.

Before mailbox move, first take full source DB backup, then enable circular logging on target DB, start moving the mailboxes. After mailbox move disable circular logging, take target db back up. Skip corrupt items. Plan to do it during weekend.

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ruhkusAuthor Commented:
Yeah, it's an older server (>5 years) and is using SATA 7.5k drives which doesn't help things. My big concern though is the extensive time it's taking to move a mailbox. As noted, four 5 gig mailboxes couldn't complete their move in a 48 hour period. It seems if I do a move during the day, it slows down mail processing, so that doesn't seem to be an option either. Even with reducing mailbox size, I don't know if it's going to complete during off-hours.
AmitIT ArchitectCommented:
That's it only way you have to go. Reducing mailbox size will surely help, in case of large mailboxes, I normally export data into multiple PST's. Then remove all data from the mailbox, move the empty mailbox and merge PST's again. I know, it is a tedious task, however it completes pretty fast.
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