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Promise Technology Pegasus R6 - Page 89

Promise Technology Pegasus R6
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Chapter 4: Technology Background
81
RAID 6 – Block and Double Parity Stripe
RAID level 6 stores dual parity data is rotated across the physical drives along
with the block data. A RAID 6 logical drive can continue to accept I/O requests
when any two physical drives fail.
Figure 5. RAID 6 stripes all drives with data and dual parity
Hence, a RAID 6 logical drive with (7) 100 GB physical drives has a capacity of
500 GB. A RAID 6 logical drive with (4) 100 GB physical drives has a capacity of
200 GB.
RAID 6 becomes more capacity efficient in terms of physical drives as the
number of physical drives increases.
RAID 6 provides double fault tolerance. Your logical drive remains available when
up to two physical drives fail.
RAID 6 is generally considered to be the safest RAID level.
A RAID 6 on Pegasus R4 consists of four physical drives.
A RAID 6 on Pegasus R6 consists of four to six physical drives.
Recommended Applications for RAID 6:
Accounting and Financial
Database servers
Any application requiring very high availability
Advantages Disadvantages
High Read data transaction rate
Medium Write data transaction
rate
Good aggregate transfer rate
Safest RAID level
High disk overhead – equivalent
of two drives used for parity
Slightly lower performance than
RAID 5
Double Distributed (Wide-space Q+Q) Parity
Physical Drives
Data
Blocks

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