Redundant Arrays of Inexpensive Disks - RAID 4-5-6-10 (Continued)RAID 4
Stripes data at a block level across several drives, with parity stored on one drive. The parity information allows recovery from the failure of any single drive. The performance of a level 4 array is very good for reads (the same as level 0). However, writes require that parity data be updated each time. This slows small random writes, in particular, though large writes or sequential writes are fairly fast. The cost per megabyte of a RAID 4 array can be low because only one drive in the array stores redundant data.
RAID Level 5 - is most often referred to as striping with distributed parity. RAID 5 is similar to level 4, but distributes parity among the drives. No single disk is devoted to parity. This can speed small writes in multiprocessing systems. Because parity data must be distributed on each drive during reads, the performance for reads tends to be considerably lower than a level 4 array. The cost per megabyte is the same as for level 4.
RAID 6 can be thought of as "RAID 5, but more". It stripes blocks of data and parity across an array of drives like RAID 5, except that it calculates two sets of parity information for each parcel of data. The goal of this duplication is solely to improve fault tolerance; RAID 6 can handle the failure of any two drives in the array while other single RAID levels can handle at most one fault. Performance-wise, RAID 6 is generally slightly worse than RAID 5 in terms of writes due to the added overhead of more parity calculations, but may be slightly faster in random reads due to spreading of data over one more disk. As with RAID levels 4 and 5, performance can be adjusted by experimenting with different stripe sizes.
RAID 10 or 0/1 - is a dual level array that utilizes multiple RAID 1 (mirrored) sets into a single array. Data is striped across all mirrored sets. As a comparison to RAID 5 where lower cost and fault tolerance is important, RAID 10 utilizes several drives, in order to provide better performance. Each drive in the array is duplicated (mirrored). This eliminates the overhead and delay of parity. This level array offers high data transfer advantages of striped arrays and increased data accessibility (reads). System performance during a drive rebuild is also better than that of parity based arrays, since data does not need to be regenerated from parity information, but copied from the other mirrored drive.
RAID 50 or 0/5 - a dual level array that utilizes multiple RAID 5 sets into a single array. In RAID 0/5 array, a single hard drive failure can occur in each of the RAID 5 without any loss of data on the entire array. Keep in mind, as the number of hard drives increase in an array, so does the increased possibility of a single hard drive failure. Although there is an increased write performance in RAID 50 , once a hard drive fails and reconstruction takes place, there is a noticeable decrease in performance, data/program access will be slower, and transfer speeds on the array will be effected.
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