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Because of how Exchange handles backup and restore operations, it may make sense to create more than one database or storage group to govern how data is grouped and backed up.
Exchange 2000 and 2003 Enterprise Edition allow the creation of multiple storage groups, as well as multiple databases within those storage groups. Exchange Standard Edition allows for one storage group and two databases.
A common reason for creating more than one storage group is so you can perform multiple simultaneous backup/restores. If you want to have a revolving backup schedule in which one storage group is backed up and then another, the fact that users' mailboxes are distributed across multiple storage groups and databases means there's much less interruption of service.
Another good reason for doing this is if you want to have discrete logs for more granular recovery operations; if one mailbox goes down, you only have to replay logs for that particular storage group or database, not everything at once.
There are two things you need to consider when setting up multiple storage groups or databases though:
- Each storage group should be placed on a different physical disk if possible. Using multiple databases and storage groups helps increase parallelism, but any benefits you'd get from that would be killed by putting them all on the same physical disk. (This also goes for putting the logs on the same disk as their corresponding databases.)
- Each additional storage group or database will require STORE.EXE to allocate a fairly significant amount of memory. Estimates vary, but each database requires approximately 10 MB; each storage group requires at least 100 MB (although that's held as virtual address space and not live RAM).
About the author: Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter and a regular contributor to SearchExchange.com.
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In regards to using different disks -- what difference does having RAID 5 make? It seems few would be running Exchange without a RAID.
—Gary L.
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It makes sense to run Exchange in a RAID setup, if possible. There may be people on a very tight budget or working with older hardware who don't have the option. RAID 5 provides both data security and parallelism, so having RAID 5 obviates to a fair degree the need to put things on different disks.
—Serdar Yegulalp, tip author
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Here is an example of a RAID configuration on a SAN.
Three Storage groups with three message stores in each to maintain a user base of 250 mailboxes per store. This helps when running maintenances as well.
EMC SAN Raid Group Configs
RG1 - (10HDs,R10)-SG1(100GB),L1(5GB)= 105GB
RG8 - (10HDs,R10)-SG2(100GB),L2(5GB)= 105GB
RG9 - (10HDs,R10)-SG3(100GB),L3(5GB), Maintenance(70GB)= 175GB
Note:
Databases on E:\
mountpoints
\SG1
\SG2
\SG3
\Maintenance
Logs on F:\
Mountpoints
\L1
\L2
\L3
—Kay G.
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