Robert’s Rules of Exchange: Multi-Role Servers

@pesos - Great comment, and a great point to reiterate.  Microsoft is going with the JBOD storage solution as our #1 recommendation, but that is only for the Exchange data storage - your databases, the associated log files and the system files used by the ESE database (the checkpoint file, etc.).  The operating system files, the Exchange binaries, etc. are recommended to be stored on storage that is protected with RAID.  As you called out, a simple mirror of the OS disk is inexpensive, and ensures that if a disk fails that has the OS on it, you are not required to rebuild your server from scratch.  For implementations where your data volumes are presented to Exchange through "mount points", the directories where you mount those volumes would also be on this system disk, and therefore protected by RAID.

Once again, only the Exchange data goes on disks that are JBOD, and only in situations where you have a minimum of 3 HA copies of the data in a DAG.  Since you have 3 HA copies (HA meaning "non-lagged") of the data online at all times in this situation, the loss of a single disk causes an unplanned switchover of a single database (approximately a 30 second outage to the users on that database), and then the administrative team would replace the failed disk, format, mount, and finally reseed to that disk to bring it back into use by Exchange.

One last thing - Microsoft is also recommending SAS as the controller for the "big cheap disks" because we see a better time between failure, and slightly higher performance from the SAS disks as opposed to the SATA disks.  The 7200 RPM SATA disks are certainly supported, but we prefer the SAS and that is what we recommend to customers when we are designing their systems.

Great comment, @pesos and everyone else!  Keep them coming!!