Chapter 16 Resiliency and Automation Strategies

Question 1

Raid 0

Answer 1

RAID 0 (also known as a stripe set or striped volume) splits (“stripes”) data evenly across two or more disks, without parity information, redundancy, or fault tolerance. Since RAID 0 provides no fault tolerance or redundancy, the failure of one drive will cause the entire array to fail; as a result of having data striped across all disks, the failure will result in total data loss. This configuration is typically implemented having speed as the intended goal.

Question 2

Raid 1

Answer 2

RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks. This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk. This layout is useful when read performance or reliability is more important than write performance or the resulting data storage capacity.

Question 3

Raid 2

Answer 3

RAID 2, which is rarely used in practice, stripes data at the bit (rather than block) level, and uses a Hamming code for error correction. The disks are synchronized by the controller to spin at the same angular orientation (they reach index at the same time[16]), so it generally cannot service multiple requests simultaneously.[17][18] However, depending with a high rate Hamming code, many spindles would operate in parallel to simultaneously transfer data so that “very high data transfer rates” are possible[19] as for example in the DataVault where 32 data bits were transmitted simultaneously.

Question 4

Raid 3

Answer 4

RAID 3, which is rarely used in practice, consists of byte-level striping with a dedicated parity disk. One of the characteristics of RAID 3 is that it generally cannot service multiple requests simultaneously, which happens because any single block of data will, by definition, be spread across all members of the set and will reside in the same physical location on each disk. Therefore, any I/O operation requires activity on every disk and usually requires synchronized spindles.

Question 5

Raid 4

Answer 5

RAID 4 consists of block-level striping with a dedicated parity disk. As a result of its layout, RAID 4 provides good performance of random reads, while the performance of random writes is low due to the need to write all parity data to a single disk,[21] at least as long as the filesystem is not RAID 4-aware and compensates for that.

Question 6

Raid 5

Answer 6

RAID 5 consists of block-level striping with distributed parity. Unlike in RAID 4, parity information is distributed among the drives. It requires that all drives but one be present to operate. Upon failure of a single drive, subsequent reads can be calculated from the distributed parity such that no data is lost.[5] RAID 5 requires at least three disks.

Question 7

Raid 6

Answer 7

RAID 6 extends RAID 5 by adding another parity block; thus, it uses block-level striping with two parity blocks distributed across all member disks.