RAID (Redundant Array of Independent Disks)

RAID

(Redundant Array of Independent Disks)

RAID 0:

RAID 0 provides no fault tolerance or redundancy. Requires a minimum of 2 disks. The information is spread across each drive (for example: as it fills one block then adds data to the next sequential block). 

RAID 0 is striping with no parity. If one drive fails, all the information is lost, unless you have a backup of the data.

This form of RAID is used for performance, multiple heads reading/writing at the same time.

Both drives should be of the same size and speed. If you have two 320 GB drives, theoretically you would have 640 GB of storage space using this configuration. 

RAID 0 is best used for video and audio streaming. It could also be used for something like a backup server. The actual backups are stored on other media than the system running the backup software. 

RAID 1:

RAID 1 requires 2 drives and is known as mirroring. The exact same data is written to both drives. With RAID 1 you can add another disk controller, this eliminates a single point of failure. Using two disk controllers in this configuration is known as duplexing.

If you are using two 320 GB drives, theoretically you will have 320 GB for storage. 

If one drive fails, all the data is retained on the other drive. You do not have to shut this system down to replace the failed drive. Simply remove the drive, take it out of the sled/carrier, and replace it with a new drive. Reinsert the drive, go to the console, and select rebuild array. 

Use this RAID configuration for operating systems, authentication servers. etc. You have minimal drive space to work with. 

RAID 5:

RAID 5 requires a minimum of 3 disks and is striping with one parity stripe. The equivalent of one drive is used for the parity information. This helps provide fault tolerance.

RAID 5 has great read performance as multiple heads read at the same time. As you increase the number of drives, so does the read speed. The write performance is slow due to the parity calculation on the full stripe. 

This RAID setup can afford the loss of only one drive, more than one drive, the data is lost. Remove the failed drive while the system is operational, install a new drive, go to the console, and select rebuild array. The performance will degrade slightly as it rebuilds the array. 

For three 320 GB drives, you will have 640 GB of storage space as the parity data will take up the equivalent of one drive.

RAID 6:

  

RAID 6 requires a minimum of 4 drives. It is configured as striping with dual parity. The equivalent of two drives is used for the parity information. This setup provides fault tolerance.

It has great read speed as multiple heads are reading at the same time. Write speed is even slower than RAID 5 as RAID 6 has to calculate dual parity for each stripe. 

RAID 6 can survive the failure of two simultaneous drives. Again take out the failed drive or dives, replace them with new drives. After reinserting the drives, go to the console and select rebuild array. 

Four 320 GB drives in a RAID 6 will give you 640 GB of storage space.