Raid And Data Protection - ZyXEL Communications NAS326 User Manual

stripped across three disks (A1 to A3 in the first strip for example) with parity information (AP) on the
fourth disk.
Table 54 RAID 5
A1 A2
B1 B2
C1 CP
DP D1
DISK 1 DISK 2
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.
Chapter 5 Storage Manager
A3 AP
BP B3
C2 C3
D2 D3
DISK 3 DISK 4
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