Adaptec RAID 3805 8-port SATA and SAS Controller Review

Raid Basics

To start, lets get a handle on what raid is and some common implementations. Raid configurations come in many shapes and sizes. The first configurations were primarily meant to allow large partitions that spanned multiple physical devices and to provide some fail safety. Choosing a raid level depends on the intended purpose for your array.

Gamers should obviously focus strictly on performance. Redundancy is usually not a requirement since your array should primarily consist of your applications installations. The root drive is usually reserved for the operating system and state files generated by the game. If the array fails, no big deal, reinstall your game. Multimedia and DVR setups should focus on both total array size and dependability via parity drives. Nearly all raid configurations require identical drives sizes.

Raid0	Striped Disk Array Data is written in even chunks to all drives. This allows large chunks to be written simultaneously in some cases. Seek times are also decreased because of the read speeds available. 2 or more drives are needed for Raid0. The effective read and write speeds are typically N times a single drives rate. Size of the array is N times a single drives space.
Raid1	Mirrored Array Data is written to multiple drives at the same time. Some Raid1 implementations will allow for raid0 like read speeds however still limit write speeds to that of a single drive. This is the most basic array for redundancy. The total size of the array is the same size as a single drive.
Raid5	Striped with Distributed Parity Raid 5 is a very common configuration in enterprise environments since it yields a large array size while maintaining significant speed benefits over a single drive. Chunks and parity are written in an alternating fashion to each drive. If a drive fails, the array will still function with reduced speed until a working drive is added back to the array. You must have 3 or more drives for this configuration.
Raid6	Striped with Dual Distributed Parity This configuration is used when data integretity is of the up-most concern. It shares the same characteristics with Raid5 however two drives can fail and slightly less performance is observed across the board. When using large drives, rebuilding can take a significant amount of time. Raid6 helps reduce of the risk of dual drive failure. Total disk space is reduced. 4 or more drives are required for this configuration.
Raid10	Stripes of Mirrors Raid10 combines the benefit of Raid0 with the safety of Raid1. 2 drives are mirrored and then stripped with other mirrored sets. This setup yields outstanding performance however available space is reduced. Raid10 also allows multiple drives to fail, as they are not in the same mirror. Drives must be added in multiples of 2’s with a minimum of 4.

There are many other raid configurations available. Some worth taking a look at are raid50 and raid60. These are effectively stripes of raid5 and raid6 arrays. These configurations can allow even more failures while still providing the performance benefits of straight striping. Other raid levels such as raid3 and raid4 are not as common anymore. Some manufactures go to great lengths to make proprietary enhancements to basic raid configurations which can slightly alter their performance under various tests. A common example of this is raid1 and read performance. Some Raid1 cards will allow both striped reads and concurrent seeks.

Nearly all raid implementations are static in that they cannot be changed unless they are reinitialized. Most array types do not support additions or subtractions into the array other than spares and failures. The bounding factor here is that the raid hardware resides at a lower level than the file system which only interacts with operating system drivers.

This particular line of cards support RAID Levels 0, 1, 10, 5, and 50. They also support more advanced raid modes such as 1E (Mirror with striped reading), 5EE (Raid5 with hotspace), 6 and 60 (dual disk parity striped across multiple raid 6 volumes). Not all cards support these raid modes so its important to check the supported modes before you purchase. These Unified Serial cards have a very nice set to choose from and its unlikely you will need any other raid mode.

One of the other nice features this line has is background initialization which allows a raid array to be built in the background even while the array is in use. Automatic and hot rebuilding is also supported which is a nice feature for systems that require serious uptime. With lower grade controllers, the system must be halted and sit in the bios until the raid array is rebuilt and back online.