System information

[5] RAID level 1 c o mes at a hig h c o st b ecause yo u write the same info rmatio n to all o f the d isks in the
array, p ro vid es d ata reliab ility, b ut in a much less sp ace-efficient manner than p arity b ased RAID levels
suc h as level 5. Ho wever, this sp ace ineffic iency co mes with a p erfo rmanc e b enefit: p arity-b ased RAID
levels co ns ume c o ns id erab ly mo re CPU p o wer in o rd er to g enerate the p arity while RAID level 1 simp ly
writes the s ame d ata mo re than o nce to the multip le RAID memb ers with very little CPU o verhead . As
suc h, RAID level 1 c an o utp erfo rm the p arity-b ased RAID levels o n machines where so ftware RAID is
emp lo yed and CPU reso urces o n the mac hine are co nsistently taxed with o p eratio ns o ther than RAID
ac tivities.
[6 ] Parity info rmatio n is calculated b ased o n the co ntents o f the rest o f the memb er d is ks in the array.
This info rmatio n c an then b e used to reco nstruc t d ata when o ne d isk in the array fails. T he
rec o nstruc ted d ata can then b e used to satisfy I/O req ues ts to the failed d isk b efo re it is rep lac ed and
to rep o p ulate the failed d isk after it has b een rep lac ed .
Red Hat Ent erprise Lin ux 6 St orage Admin ist rat io n G uide
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