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Trying to understand Exchange databases RRS feed

  • Question

  • I'm a complete Exchange newbie, and I'm trying to determine why you would have more than one database on an Exchange 2010 server (DAG aside.)  Is it partially for performance reasons, you put some of your DBs on one drive, some on another, and Exchange then uses both to "split the load?"  Or do some features require their own DB, such as public folders vs mail?

    DAG I kind of get, it sounds like it is log-shipping replication between two or more Exchange servers, and each DB counts against the total on a server (So a 2 server Exchange with DAG could "host" a max of 5 "live" DBs between the two servers {2 live and 2 copies each + 1 live with a copy on the second})

     

    Thank you,

    Jason A.

    PS  Yes, I know Exchange is rather a lot to try to "self-teach," but such is my lot...


    Jason A.
    Monday, October 3, 2011 6:55 PM

Answers

  • Separate the DAG from the number of databases.
     
    You have more than one database when your database reaches a particular size or your backup software can’t back it up in sufficient time or when your disk subsystem can’t handle the number of IO that you need. If any one (and there are other reasons) of those factors kicks in you get some more spindles and then build out a new store.
     
    In E2010 a 2TB store is no problem but you might find that you run out of IO on a disk way before you have the number of users that gets to 2TB of email. That’s the easy part. Now, the DAG.
     
    The DAG is there for HA purposes. Back in 2003 Exchange was stable enough that you only needed the one copy of the database and could do your patching in a small enough window that it didn’t matter. Fast forward to 2010 you have people clamouring for email 24/7. No maintenance window exists and even backups (if done) compete with user time and online maintenance time. So to prevent outages and allow backups (if you are just running DAS rather than an intelligent SAN based storage) you really need a better solution; one which allows backups to be done elsewhere and where a failover to another copy of the same store.
     
     
     
     
     
    "Jason A_" wrote in message news:f1120a47-7d27-4a47-9271-cc218f2e720b...

    I'm a complete Exchange newbie, and I'm trying to determine why you would have more than one database on an Exchange 2010 server (DAG aside.)  Is it partially for performance reasons, you put some of your DBs on one drive, some on another, and Exchange then uses both to "split the load?"  Or do some features require their own DB, such as public folders vs mail?

    DAG I kind of get, it sounds like it is log-shipping replication between two or more Exchange servers, and each DB counts against the total on a server (So a 2 server Exchange with DAG could "host" a max of 5 "live" DBs between the two servers {2 live and 2 copies each + 1 live with a copy on the second})

     

    Thank you,

    Jason A.

    PS  Yes, I know Exchange is rather a lot to try to "self-teach," but such is my lot...


    Jason A.

    Mark Arnold, Exchange MVP.
    • Marked as answer by Jason A_ Monday, October 3, 2011 9:04 PM
    Monday, October 3, 2011 7:46 PM

All replies

  • Separate the DAG from the number of databases.
     
    You have more than one database when your database reaches a particular size or your backup software can’t back it up in sufficient time or when your disk subsystem can’t handle the number of IO that you need. If any one (and there are other reasons) of those factors kicks in you get some more spindles and then build out a new store.
     
    In E2010 a 2TB store is no problem but you might find that you run out of IO on a disk way before you have the number of users that gets to 2TB of email. That’s the easy part. Now, the DAG.
     
    The DAG is there for HA purposes. Back in 2003 Exchange was stable enough that you only needed the one copy of the database and could do your patching in a small enough window that it didn’t matter. Fast forward to 2010 you have people clamouring for email 24/7. No maintenance window exists and even backups (if done) compete with user time and online maintenance time. So to prevent outages and allow backups (if you are just running DAS rather than an intelligent SAN based storage) you really need a better solution; one which allows backups to be done elsewhere and where a failover to another copy of the same store.
     
     
     
     
     
    "Jason A_" wrote in message news:f1120a47-7d27-4a47-9271-cc218f2e720b...

    I'm a complete Exchange newbie, and I'm trying to determine why you would have more than one database on an Exchange 2010 server (DAG aside.)  Is it partially for performance reasons, you put some of your DBs on one drive, some on another, and Exchange then uses both to "split the load?"  Or do some features require their own DB, such as public folders vs mail?

    DAG I kind of get, it sounds like it is log-shipping replication between two or more Exchange servers, and each DB counts against the total on a server (So a 2 server Exchange with DAG could "host" a max of 5 "live" DBs between the two servers {2 live and 2 copies each + 1 live with a copy on the second})

     

    Thank you,

    Jason A.

    PS  Yes, I know Exchange is rather a lot to try to "self-teach," but such is my lot...


    Jason A.

    Mark Arnold, Exchange MVP.
    • Marked as answer by Jason A_ Monday, October 3, 2011 9:04 PM
    Monday, October 3, 2011 7:46 PM
  • So it sounds like I was on the right track.

    Multiple DBs are used for performance purposes, backup purposes (hadn't thought about that one,) and if you reach the size limit of the DB itself.

    DAG is primarily for maintaining uptime of the e-mail system, more than any sort of disaster recovery, although I would presume it could be used for that as well, by having your Exchange servers in separate locations.

     

    Thanks!

    Jason A.


    Jason A.
    Monday, October 3, 2011 7:52 PM