Understanding RAID Concepts and Levels
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RAID 1
Also known as a mirrored array. Mirroring is done on pairs of drives.
Mirrored disk arrays write data to two drives using RAID 1 algorithms (see
Figure 2). This gives your system fault tolerance by preserving the data on
one drive if the other drive fails. Fault tolerance is a basic requirement for
mission critical systems like web and database servers.
3ware uses a patented technology, TwinStor®, on RAID 1 arrays for
improved performance during sequential read operations. With TwinStor
technology, read performance is twice the speed of a single drive during
sequential read operation.
The adaptive algorithms in TwinStor technology boost performance by
distinguishing between random and sequential read requests. For the
sequential requests generated when accessing large files, both drives are used,
with the heads simultaneously reading alternating sections of the file. For the
smaller random transactions, the data is read from a single optimal drive head.
Figure 2. RAID 1 Configuration Example
RAID 5
Combines striping data with parity (exclusive OR) to restore data in case of a
drive failure. This array type provides performance, fault tolerance, high
capacity, and storage efficiency. Requires a minimum of three drives.
Parity information is distributed across all drives rather than being
concentrated on a single disk (see Figure 3). This avoids throughput loss due
to contention for the parity drive.
Figure 3. RAID 5 Configuration Example
RAID 5
A Blocks
0 parity
A4
A3
A2
A1
1 parity
B4
B3
B2
2 parity
C4
C3
C1
3 parity
D4
D2
D1
4 parity
E3
E2
E1
B0
C0
D0
E0
B Blocks C Blocks D Blocks
E Blocks
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