Transaction Logs – Backups

LukeQuake

Something that I’m having trouble understanding at the moment is the following. How is that if you do a full restore of a mailstore then roll forward using the latest transaction logs you completely restore the data in user’s mailboxes?

Where do transactions log come into the process? What exactly do they contain?

Thanks,

geekie

Hopefully this link should answer your question.

http://www.microsoft.com/technet/prodtechnol/exchange/guides/UseE2k3RecStorGrps/d42ef860-170b-44fe-94c3-ec68e3b0e0ff.mspx?mfr=true

LukeQuake

So the transaction logs are written to before the database is? Therefore, if the database fails you can restore to the latest transaction logs and carry on without looking any data. However, wouldn’t there be a massive different between a database that was backed up the previous evening and the most recent transaction log if the server went down in the middle of the day? What is the impact on a server whilst it 'catches' up?

geekie

So the transaction logs are written to before the database is? Therefore, if the database fails you can restore to the latest transaction logs and carry on without looking any data.

Yes, Exchange writes changes to the logs first and then to the database. Each transaction log is 5mb in size and once full Exchange will then create a new log.

If the DB fails or stops, changes are not lost. One can replay the logs which will apply any changes which have not yet been written to the DB.

LukeQuake

Thanks for the help!