Acer SmartRAID V Bedienungsanleitung Seite 189

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Theory of Operation
Degraded Mode
When a drive fails in a RAID 0 array, the entire array fails. In a RAID 1
array, a failed drive reduces read performance by 50%, as data can only be
read from the remaining drive. Write performance is increased slightly
because only one drive is accessed. A RAID array operating with a failed
drive is said to be in degraded mode.
RAID 5 arrays synthesize the requested data by reading and XORing the
corresponding data stripes from the remaining drives in the array. For
RAID 5, the magnitude of the performance impact in degraded mode
depends on the number of drives in the array. An array with a large
number of drives will experience more performance degradation than an
array with small number of drives.
Rebuilding a Failed Hard Drive
A failed drive can be replaced in a RAID 1 or RAID 5 array by physically
removing the drive and replacing it or by a designated Hot Spare.
SmartRAID V controllers will rebuild the data for the failed drive onto the
new drive or Hot Spare. This rebuild operation occurs online while normal
host reads and writes are being processed by the array.
RAID 1 arrays are rebuilt relatively quickly, because the data is simply
copied from the duplicate (mirrored) drive to the replacement drive. For
RAID 5 arrays, the data for the replacement drive must be synthesized by
reading and XORing the corresponding stripes from the remaining drives
in the array. RAID 5 arrays that contain a large number of drives will
require more time for a rebuild than a small array.
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