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How Are RAID Level Choices Made?
By Tim Arland, Principal Consultant for Storage Solutions, Forsythe Solutions Group Inc. , October 19, 2007, 3:05 PM RAID levels not only apply the appropriate level of protection for data, they also have a tremendous effect on the performance of...
October 20, 2007
1 Min Read
RAID levels not only apply the appropriate level of protection for data, they also have a tremendous effect on the performance of most applications. There are some effective practices guidelines, but each application in each organization must be analyzed to ensure adherence to business impact and performance metrics developed by the business and technical groups.
RAID (Redundant Array of Independent Disks) is a standard method to add protection to data sets by adding redundancy in the underlying physical disks. Configured properly, any RAID set (except RAID 0) should be able to handle the loss of one disk without affecting users' ability to access data.
RAID 1 (mirroring) and RAID 5 (striped parity) are the most common implementations of RAID.
Each RAID implementation has different protection and performance properties. As storage administrators and application owners analyze the application data sets to determine the appropriate RAID level, the following should be considered:
Application criticality. Mission-critical applications should exist on RAID sets that maximize protection and reduce rebuild time in the event of failure.
Application performance. Applications that require high levels of transactional performance, such as OLTP databases, should utilize RAID sets that maximize performance for write operations.
Disk failure. Assume that multiple disks will inevitably fail in any given array or RAID configuration. Although the statistical chances of this are low, it does happen. Make sure that your mission-critical RAID-protected storage is also protected with array or host-based replication and backups.
Spindle count and parity. Some applications, like Microsoft Exchange, are very particular about spindle count and parity calculations as they pertain to overall write response performance. Always make sure to refer to vendor specifications and best practices before you make a final determination for RAID protection.
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