RAID 1
Raid 1 - Duplexing or 'Mirroring'
RAID 1 consists of two drives. The second is an exact copy of the first, and offers greater reliability because of the fact there are two copies of the data.
Data is read in a similar way to RAID 0 by reading data simultaneously. The first block read from disk 0 and the second block from disk 1 (see diagram). Because there are two write cycles, this slows down data storage.
Typical uses for RAID 1 would be situations were there are more reads than writes to the media and, should a drive fail, redundancy is necessary so the system keeps running. For example, web servers.Advantages of RAID 1
- Fast data reads
- Good redundancy - if one drive fails, the system continues to run.
Even though there is redundancy in RAID 1, regular backups are critical.
Disadvantages of RAID 1
- Double the cost of a similar RAID 0 system
- Writes to disk take twice as long as a single drive system
- Reduced storage space as 50 percent of the total is used for redundancy
Most RAID 1 systems allow for 'Hot Spares' - this allows 1 or 2 spare drives to be placed on the RAID controller, so that in the case of a drive failure. The Hot spare will replace the failed drive and will rebuild itself with the data from the remaining good drive.