HP 381513-B21 HP Smart Array Controller technology, 3rd edition - Page 15

Table 4. Recommended stripe sizes Type of server application Mixed read/write Mainly sequential read (such as audio/video applications) Mainly write (such as image manipulation applications) Suggested stripe size change Accept default value Larger stripe sizes Smaller stripes for RAID 5, RAID 6 Larger stripes for RAID 0, RAID 1, RAID 1+0 NOTE: Different controllers may have different stripe sizes. Users should consult the controller user guide for more details. RAID migration Using the ACU, administrators can also change the RAID level of the logical drive without downtime. Administrators can perform RAID migration to increase raw data storage capacity, improve performance by increasing the number of spindles in a logical drive, or change fault tolerance (RAID) configurations. Table 5 summarizes RAID levels and the amount of space required for each type of fault tolerance. Table 5. Summary of RAID methods Usable drive space* RAID 0 (striping) 100% RAID 1 (mirroring) 50% RAID 1+0 (striping and mirroring) 50% RAID 5 67% to 93% RAID 6 50% to 96% Usable drives N N/2 N/2 N-1 N-2 Minimum number of 1 drives Tolerant of single drive No failure? Tolerant of multiple No simultaneous drive failures? Read performance High 2 Yes No High 4 3 Yes Yes Yes, if failed drives not mirrored to each other High No High 4 Yes Yes High Write performance High Medium Medium Low Low Relative cost Low High High Medium Medium * The values for usable drive space are calculated assuming a maximum of 14 physical drives of the same capacity (or a maximum of 56 for RAID 6) with no online spares. HP recommends not exceeding these maximum figures (excluding any allowable online spares) when configuring a drive array due to the increased likelihood of logical drive failure with more disk drives. 15