Memory for disk arrays
In addition to RAID 3 dignity are slight decrease in productivity of crashes and
rapid recovery. Advantages: -- a very high data transfer speed; -- Refusal disk
little impact on the speed of work array; -- small overhead for the
implementation of redundancy. Disadvantages: -- easy implementation; -- low
productivity with high-intensity small amount of data requests. Used
infrequently because loses RAID-5 on the use of disk space. Realisation is
costly. The minimum number of drives in the array RAID-3 - 3 pc. ii. RAID 4 -
tolerant array of independent disks with shared disk parity (Independent Data
disks with shared Parity disk) RAID Level 4 - a tolerant array of independent
disks with one disk for storing amounts of control . RAID 4 is largely similar
to RAID 3, but differs from the past, first of all, much greater recordable data
block size (greater than the amount of data stored). This is the basic
difference between a RAID 3 and RAID 4. After recording a group calculated
checksum (in the same way as in the case of RAID 3), which is recorded on a
dedicated disk for this. Thanks to a greater than that of RAID 3, the block size
of several possible joint operations reading (scheme independent access). RAID 4
file transfer increases the productivity of small volume (by rasparalle-bulb
reading operations). But because the record should be calculated checksum a
dedicated disk, the simultaneous execution of operations is not possible (there
asimmetrich-of the input and output). The current standard does not provide
benefits in the near-tion with the large volume of data transmission.
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