The Message Store supports multiple store partitions. Place each partition on its own stripe or volume. The number of partitions that should be put on a store is determined by a number of factors. The obvious factor is the I/O requirements of the peak load on the server. By adding additional file systems as additional store partitions, you increase the available IOPS (total IOs per second) to the server for mail delivery and retrieval. In most environments, you will get more IOPS out of a larger number of smaller stripes or LUNs than a small number of larger stripes or LUNs.
With some disk arrays, it is possible to configure a set of arrays in two different ways. You can configure each array as a LUN and mount it as a file system. Or, you can configure each array as a LUN and stripe them on the server. Both are valid configurations. However, multiple store partitions (one per small array or a number of partitions on a large array striping sets of LUNs into server volumes) are easier to optimize and administer.
Raw performance, however, is usually not the overriding factor in deciding how many store partitions you want or need. In corporate environments, it is likely that you will need more space than IOPS. Again, it is possible to software stripe across LUNs and provide a single large store partition. However, multiple smaller partitions are generally easier to manage. The overriding factor of determining the appropriate number of store partitions is usually recovery time.
Recovery times for store partitions fall into a number of categories:
First of all, the fsck command can operate on multiple file systems in parallel on a crash recovery caused by power, hardware, or operating system failure. If you are using a journaling file system (highly recommended and required for any HA platform), this factor is small.
Secondly, backup and recovery procedures can be run in parallel across multiple store partitions. This parallelization is limited by the vertical scalability of the mboxlist directory as the Message Store uses a single set of databases for all of the store partitions. Store cleanup procedures (expire and purge) run in parallel with one thread of execution per store partition.
Lastly, mirror or RAID re-sync procedures are faster with smaller LUNs. There are no hard and fast rules here, but the general recommendation in most cases is that a store partition should not encompass more than 10 spindles.
The size of drive to use in a storage array is a question of the IOPS requirements versus the space requirements. For most residential ISP POP environments, use “smaller drives.” Corporate deployments with large quotas should use “larger” drives. Again, every deployment is different and needs to examine its own set of requirements.