When specifying storage for a server-class machine, it’s important to understand that the drives within the system will be running 24/7 for the next 4-5 years. Because of this, the equipment used must be highly reliable. In order to enhance this reliability and fault tolerance, as well as the performance, various RAID (Redundant Array of Independent Disks) configurations are used.
- RAID 1 is a mirrored set of drives, should one fail, the second drive has a full copy of your data. In a normal operating state, the mirror also provides faster access when data is being read, as the data can be read from both drives simultaneously. RAID 1 is typically used for the operating system partition of the server.
- RAID 5: in this configuration, data is spread across (striping) 3-?? drives (depending on the chassis drive capacity) and a checksum is created on one additional drive. Should one drive fail, the data on the missing drive is calculated from the checksum and remaining drives. This is typically used for large capacity storage. It is not recommended to place more than 8 drives in a RAID 5 array.
- RAID 10: in this configuration, data is spread across 4-?? drives (depending on the chassis drive capacity) and a checksum is created on one additional drive. Should one drive fail, the data on the missing drive is calculated from the checksum and remaining drives. This is typically used for large capacity storage. It is not recommended to place more than 8 drives in a RAID 5 array.
- Global hot spare: an unused drive designated to rebuild the array in real time in the event of a failure. When one of the drives is predicted to fail, or it fails, this drive takes its place, ensuring the integrity of the data and continued operation in the event of failure.
Calculate Capacity
To calculate capacity for RAID 1 configurations, multiply the size of one of the drives by 0.8. This will gie you the usable data storage capacity for that drive.
To calculate capacity for RAID 5 configurations, subtract one from the number of drives in the RAID 5 array, then multiply that number times the capacity of each drive, then multiply that result by 0.8.
The global hot spare capacity is not included in either calculation, as it is unavailable for data storage.