ZyXEL Communications NAS540, User Manual

Page: 101 / 372

Chapter 8 Storage Manager
Cloud Storage User’s Guide
101
RAID 10
RAID 10 (RAID 1+0) is a nested RAID where two RAID 1 arrays are stored on the physical disks
with a RAID 0 array on top. It is a stripe of mirrors. RAID 1 provides redundancy while RAID 0
boosts performance. The following figure shows two disks in two RAID 1 arrays. Data is duplicated
across two disks, so if one disk fails, there is still a copy of the data. These two arrays are
configured as a single RAID 0 array for faster performance
.
Typical applications for RAID 10 are those requiring both high performance and reliability such as
enterprise servers and high-end moderate-sized database systems. RAID 10 is often used in place
of RAID 1 or RAID 5 by those requiring higher performance. It may be used instead of RAID 1 for
applications requiring more capacity.
RAID 5
RAID 5 provides the best balance of capacity and performance while providing data redundancy. It
provides redundancy by striping data across three disks and keeps the parity information (AP) on
the fourth disk (in each stripe). In case of disk failure, data can be recovered from the surviving
disks using the parity information. When you replace the failed disk, the reconstructed data is
written onto the new disk. Re-synchronize the array to have it return to its original state. The
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
Table 35
RAID 10
RAID 0
RAID 1 RAID 1
A1 A1 A2 A2
A3 A3 A4 A4
A5 A5 A6 A6
A7 A7 A8 A8
DISK 1 DISK 2 DISK 3 DISK 4
Table 36
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