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manual abstract
New Advanced RAID Level for Today's Larger Storage Capacities:
2
Introduction
With a growing need for larger storage capacity, customers are demanding reliable ways to
protect large volumes of data stored across an increasing number of disk drives. RAID
technology allows a group of disk drives to be “tied” together to act like a single logical disk
drive from the operating system perspective, providing increased performance and fault tolerance.
Currently, Compaq offers very reliable RAID systems with the family of Smart Array Controllers
that support RAID 0, 1, 0+1, and 5.
For customers who wish to create large logical drives with a high number of disk drives or high
capacity disk drives they need to consider the limitation of current RAID schemes. With RAID 1,
it is expensive to create large volumes based upon the consumption of disk drives for mirroring.
With RAID 5, it is not recommended to configure a logical drive array with greater than 14 drives
due to risk of data loss.
In addition, today’s larger disk drive capacities may leave an array exposed to a considerable
amount of risk following a single disk drive failure due to the time required to rebuild the failed
drive. A second drive failure in a mirrored set in RAID 1 and any second drive failure in RAID 5
would cause an array to fail, causing data loss and downtime. With this in mind, larger capacity
disk drives present new risks due to longer drive rebuild times.
Compaq’s new Advanced Data Guarding reduces the risk of an array failure and requires far less
storage capacity overhead than RAID 1.
The following table illustrates the current RAID levels used by customers, their purposes, and
limitations, compared to the new advanced RAID level from Compaq:
Table 1. RAID levels and functions
RAID LEVEL
PURPOSE
LIMITATION
RAID 0
Increased performance when no RAID
No fault tolerance and highly vulnerable to
protection is required.
failure.
RAID 1, 0+1
Mirroring: Identical data stored on multiple
Requires 50% of capacity to be dedicated
drives, high fault tolerance, improved
to fault protection. Expensive to implement
performance.
across large volumes (doubling the cost-
per-capacity).
RAID 5
Distributed Data Guarding: Parity data is
Lower fault tolerance. Not recommended
distributed across all drives. Protects
for volumes greater than 14 drives. Too
against the failure of any one drive in an
risky for large volumes.
array. Provides improved performance at a
minimum cost.
NEW RAID ADG
Advanced Data Guarding: Two sets of
Lower performance than other RAID
parity data distributed across all drives.
levels.
Protects against the failure of any two
drives in an array. Provides high fault
tolerance at a minimum implementation
cost.
13JE-1000A-WWEN
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