I’ve been through my share of Microsoft Exchange migrations over the years. In fact, I’d like to forget migrating from versions 5.5 and older. Since Microsoft Exchange 2000 through 2010, it’s been a fairly low-risk procedure providing one follows best practices. However, one item can easily get buried in the details: Log volume sizing.
Log volumes and the importance of their respective sizing are nothing new to seasoned Microsoft Exchange gurus. But it’s almost a rite of passage for newer Microsoft Exchange techs to create and execute a seamless migration plan – then forget to stagger the mailbox moves resulting in crashed information stores and the dreaded 9559 error
For every byte of data added or changed in Exchange, the subsequent transaction is written to a log file at a 1:1 ratio. Since moving mailboxes generates a ton of logs it’s a requirement to keep the mailbox data moved below the size of your log volumes in GB. With a nightly full backup to record the transactions into the database files and flush them from the log volume, migration can continue the next day. But what if you (or your trusted co-worker) forgets and moves too much data at once? Your Microsoft Exchange server will go down hard – that’s a fact. The good thing is that simply creating space on the log volume will allow the affected database to mount. But creating space on a full volume is tough when you don’t want to delete anything. So…create something to delete! Just make a dummy file of between 3-5% of what’s available as an escape valve. If the log volume gets full simply delete it and restart the Information Store service. In fact, I call my dummy file “DELETEME.txt”
From any Windows OS running XP or later just run the following command and name the file using the full path of the log volume:
fsutil createnew <driveletter>:\<logvolumepath>\deleteme.txt 5000000000 (creates a 5GB file)
Clearly this should only be used as a method of last resort and it will only buy a small amount of time during which you will need to run a full backup immediately. But if you find yourself staring down a 9559 error with users clamoring to get their mail – this can be a real lifesaver!