The combination of striping and mirroring provides the performance RAID 0+1 benefits of RAID 0 and the redundancy benefits of RAID 1. (striped mirrors) This option is also known as RAID 1+0 and RAID 10. RAID 5 RAID 5 presents a logical disk composed of multiple physical disks with (rotated data striped across the disks in sequential blocks (stripe units). However, parity) the underlying physical disks have parity information scattered throughout the disk array, as Figure 3 shows. For read requests, RAID 5 has characteristics that are similar to those of RAID 0. However, small RAID 5 writes are much slower than those of JBOD or RAID 0 because each parity block that corresponds to the modified data block requires three additional disk requests. Because four physical disk requests are generated for every logical write, bandwidth is reduced by approximately 75%. RAID 5 provides data recovery capabilities because data can be reconstructed from the parity. RAID 5 can survive the loss of any one physical disk, as opposed to RAID 1, which can survive the loss of multiple disks as long as an entire mirrored set isn’t lost. RAID 5 requires additional time to recover from a lost physical disk compared to RAID 1 because the data and parity from the failed disk can be recreated only by reading all the other disks. Performance during the rebuilding period is severely reduced due only due to the rebuilding traffic but also because the reads and writes that target the data that was stored on the failed disk must read all disks (an entire "stripe") to re-create the missing data. RAID 5 is less expensive than RAID 1 in that it requires only the addition of a single disk per array, rather than double the total amount of disks in an array. RAID 6 RAID 6 is basically RAID 5 with additional redundancy built in. Instead of a single block of parity per stripe of data, two blocks of redundancy are included. The second block uses a different redundancy code (as opposed redundancy) to parity), which allows data to be reconstructed after the loss of any two disks. Alternatively, disks can be arranged in a two-dimensional matrix, and both vertical and horizontal parity can be maintained. Rotated redundancy schemes (such as RAID 5 and 6) are the most difficult to understand and plan for. Figure 3 illustrates RAID 5. Figure 3. RAID 5 Overview Choosing the RAID Level Each RAID level involves a trade-off between the following factors: Cost Performance Availability Reliability
RAID 0+1 (striped mirrors) The combination of striping and mirroring provides the performance benefits of RAID 0 and the redundancy benefits of RAID 1. This option is also known as RAID 1+0 and RAID 10. RAID 5 (rotated parity) RAID 5 presents a logical disk composed of multiple physical disks with data striped across the disks in sequential blocks (stripe units). However, the underlying physical disks have parity information scattered throughout the disk array, as Figure 3 shows. For read requests, RAID 5 has characteristics that are similar to those of RAID 0. However, small RAID 5 writes are much slower than those of JBOD or RAID 0 because each parity block that corresponds to the modified data block requires three additional disk requests. Because four physical disk requests are generated for every logical write, bandwidth is reduced by approximately 75%. RAID 5 provides data recovery capabilities because data can be reconstructed from the parity. RAID 5 can survive the loss of any one physical disk, as opposed to RAID 1, which can survive the loss of multiple disks as long as an entire mirrored set isn’t lost. RAID 5 requires additional time to recover from a lost physical disk compared to RAID 1 because the data and parity from the failed disk can be recreated only by reading all the other disks. Performance during the rebuilding period is severely reduced due only due to the rebuilding traffic but also because the reads and writes that target the data that was stored on the failed disk must read all disks (an entire "stripe") to re-create the missing data. RAID 5 is less expensive than RAID 1 in that it requires only the addition of a single disk per array, rather than double the total amount of disks in an array. RAID 6 redundancy) RAID 6 is basically RAID 5 with additional redundancy built in. Instead of a single block of parity per stripe of data, two blocks of redundancy are included. The second block uses a different redundancy code (as opposed to parity), which allows data to be reconstructed after the loss of any two disks. Alternatively, disks can be arranged in a two-dimensional matrix, and both vertical and horizontal parity can be maintained. Rotated redundancy schemes (such as RAID 5 and 6) are the most difficult to understand and plan for. Figure 3 illustrates RAID 5. Figure 3. RAID 5 Overview Choosing the RAID Level Each RAID level involves a trade-off between the following factors: Cost Performance Availability Reliability
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