How to choose the right RAID configuration for a new storage-area network (SAN)

Before choosing a RAID configuration for a new storage-area network (SAN), you need to consider the performance requirements of your data and the number of disks needed for an effective implementation.

Our business intends to acquire a storage-area network (SAN) this year as we want to move away from direct-attached storage (DAS). Fifty percent of our data is in a business-critical SQL database and Microsoft Exchange Server, while the other 50% consists of Microsoft Office documents. What RAID configurations should we consider for our new SAN and why?
A multiple disk tray approach is needed in this situation. You do not want to put the Office files on the fastest and most expensive disks, however the SQL data does require high performance. A fast SCSI disk tray configured as RAID 10 will give the best SQL performance, while a secondary disk tray with SATA drives configured as RAID 5 will give resilience at a much reduced cost.

With some storage-area networks it is possible to move data between these drive sets using an automated data tiering function based on user-defined file access rules. You may also be able to pin data by volume into specific disk areas so you could, for example, use the fastest disk tray for the SQL data. RAID 10 uses a stripe and mirror approach that is fast and resilient. RAID 5 stripes disks with parity providing resilience against disk failure with a one to three disk overhead.

For more information, read "RAID levels explained"

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