Adaptec GDTSETUP Manual de usuario descargar pdf (Pagina 65)

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RAID 4 works in the same way as RAID 0. The data are striped amongst the hard disks. Ad-

ditionally, the controller calculates redundancy data (parity information) which are stored

on a separate hard disk (P1, P2, ...). Even when one hard disk fails, all data are still fully

available. The missing

data is recalculated from

the data still available

and the parity informa-

tion. Unlike in RAID 1,

only the capacity of one

hard disk is needed for

the redundancy. If we

consider, for example, a

RAID 4 disk array with 5

hard disks, 80% of the

installed hard disk ca-

pacity is available as

user capacity, only 20%

is used for redundancy. In situations with many small data blocks, the parity hard disk be-

comes a throughput bottle-neck. With large data blocks, RAID 4 shows significantly im-

proved performance.

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Unlike RAID 4, the parity data in a RAID 5 disk array are striped in all hard disks. The RAID 5

disk array delivers a balanced throughput. Even with small data blocks, which are very likely

in a multi-tasking and multi-user environment, the response time is very good. RAID 5 of-

fers the same level of security as RAID 4. When one hard disk fails, all data are still fully

available, the missing data are recalculated from the data still available and the parity in-

formation. RAID 4 and RAID 5 are particularly suitable for systems with medium to large

capacity requirements,

due to their efficient

ratio of the installed

and actually available

capacity.

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Adaptec GDTSETUP Manual de usuario Pagina 65