ZyXEL Communications NAS Series, Руководство пользователя

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Chapter 4 Web Configurator Basics
Cloud Storage User’s Guide
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following example shows data stripped across three disks (A1 to A3 in the first strip for example)
with parity information (AP) on the fourth disk
.
The capacity of a RAID 5 array is the smallest disk in the RAID set multiplied by one less than the
number of disks in the RAID set. For example, if you have four disks of sizes 150 GB, 150 GB, 200
GB and 250 GB respectively in one RAID 5 array, then the maximum capacity is 450 GB (3 * 150
GB, the smallest disk size) and the remaining space (300 GB) is unused.
Typical applications for RAID 10 are transaction processing, relational database applications,
enterprise resource planning and other business systems. For write-intensive applications, RAID 1
or RAID 1+0 are probably better choices, as the performance of RAID 5 will begin to substantially
decrease in a write-heavy environment.
Hot-spare
A RAID 1 or RAID 5 array with a hot-spare operates as a three-disk RAID 1 or RAID 5 array with the
fourth disk on standby. The standby disk automatically comes into play if a disk in the array fails.
The advantage of a hot-spare is that if a disk fails, then the array resynchronizes automatically with
the standby disk and operates at healthy array speed after the resynchronization.
Note: You need four hard disks installed to use RAID 10, RAID 5 or RAID 5 with hot-
spare.
RAID and Data Protection
If a hard disk fails and you’re using a RAID 1, RAID 10, or RAID 5 array then your data will still be
available (but at degraded speeds until you replace the hard disk that failed and re-synchronize the
array). However, RAID cannot protect against file corruption, virus attacks, files incorrectly deleted
or modified, or the NAS malfunctioning.
Table 26
RAID 5
A1 A2 A3 AP
B1 B2 BP B3
C1 CP C2 C3
DP D1 D2 D3
DISK 1 DISK 2 DISK 3 DISK 4