The tape RAID Option lets you implement a redundant array of independent devices (RAID) technology in your CA ARCserve Backup environment, using multiple drives to simultaneously process data during backup and restore operations. It writes data across all the drives in the array, in a predefined order. Each drive array appears on all informational screens as a single virtual drive.
The option supports RAID levels 0, 1, and 5:
The following table describes and compares the various modes used by RAID:
|
RAID Level |
Description |
|
RAID Level 0 |
Data striping transparently distributes data over multiple drives to make them appear as a single, high-performance drive. This involves spreading out blocks of each file across multiple disks. Data striping uses parallel data processing to provide high throughput performance. Although data striping provides high performance by allowing data to be processed in parallel, it does not provide fault tolerance. If a single drive in a RAID level 0 array fails, all data is lost; in the case of RAID tape drives, the backup is not available because of the drive failure. RAID level 0 is an ideal solution when you require optimum throughput and fault tolerance is not an issue. If fault tolerance is required, you must use RAID level 1 or RAID level 5. |
|
RAID Level 1 |
Tape Mirroring allows you to maintain two copies of backup data; one is typically maintained at the backup location and the other is located safely off site. It combines two physical disks into a single array. Data is written to or read from both drives at the same time. RAID 1 provides fault tolerance and reliability, by allowing you to maintain two copies of backup data: one that is typically maintained at the backup location and the duplicate or mirrored copy located safely at another site. You can use this RAID level to transport your data easily without performing a media copy operation. In the mirroring mode, the operations of the drives are duplicated. Whenever data is written to one drive, the same data is also written to the redundant drive, so there are always two copies of the data. The redundant drive ensures that the backup is completed, even if a drive or media fails. In case of drive failure, the backup or restore continues with the remaining drive. A session cannot be appended to a RAID-1 tape in a stand-alone drive. Note: RAID 1 is also referred to as disk mirroring or duplexing. Mirroring uses one channel and duplexing uses two channels. |
|
RAID Level 5 |
Parity is an error-detection method used to detect and correct errors in data transmissions by performing specific checks of the data blocks within a stripe. In the event of a single drive failure, the information for the missing drive or media can be recreated by examining the remaining data and the parity information. This information enables the system to regenerate the missing data bits RAID 5 incorporates data striping. With a RAID 5 array using three or more drives, data and parity are striped across all the drives. Data is processed on two drives while the third drive holds the parity information. If one of the data drives is lost, the parity information ensures that the missing data can be recreated. RAID 5 combines good performance, fault tolerance, high capacity, and storage efficiency. Because of the need for the system to calculate parity information during write activity, RAID 5 is best suited to situations where read activity is much higher than write activity. (For situations where write activity is high, RAID 1 is probably a better choice). |
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