HP AutoRAID 12H manual Super redundancy, Enhances RAID

section 2			“hp extends virtualization to the array”
			—by D.H. Brown Associates, Inc.
VA7000 virtualization, managed at the array			super redundancy		2
level, offers the advantage of providing greater			enhances RAID
granularity when managing a pool of logical
storage. Logical Unit Name (LUN) capacity is
definable as a logical set of storage blocks rather			As alternatives to the “self-tuning” LUN-management
			capability described above, the VA7000 series
than as a specific set of predefined physical disks.
			also enhances LUN performance through its use
Each LUN becomes scalable from a few
			of RAID configurations “redundancy groups.”
megabytes to several terabytes by adding
capacity without operator intervention (the array			Many variations to RAID	configurations have
automatically controls the addition of new
			surfaced over the past 10 years. Most provide
capacity to the storage pool).
This “self-tuning” capability automatically			moderate variations on the standard RAID 1
restripes data across new disks added to the			(mirroring) and RAID 5 (striping) techniques.
array, minimizing any potential imbalances of			In its VA7000 Series, HP delivers a variation that
data distribution within the VA7000 series.			substantially adds to its availability characteristics.
Redistribution occurs in the background with no			RAID 5DP (Double Parity) approaches a RAID 6
impact on SAN bandwidth or server performance.			solution in that it enables recovery from simultaneous
This function significantly reduces the efforts			failures in two disks without loss of any data.
required by the system administrator to keep
storage resources in balance.			While this might seem superfluous in RAID arrays
Also with VA7000 virtualization, the number of			of only a few disks, it	becomes	critical	in
			configurations supporting	a large	number	of
LUNs is no longer restricted by the amount of
			disks in a virtual array. The potential for disruption
physical storage. Administrators can configure
			due to disk failure grows	with the	number	of
LUNs up to the limit permitted by the architecture
			disks involved in an array. The goal of virtualization
without concern for	physical	disk groupings
			is to remove the physical constraints, which
within arrays.
			enables dozens of disks to be used in a single
Disk arrays without virtualization support LUNs			virtual array. HP has addressed this concern
			with its RAID 5DP solution, increasing data
only from contiguous free space, requiring allocation
of large storage chunks even if only a small portion			availability by two orders of magnitude over
is necessary. As changes occur over time, data			traditional RAID 5 implementations. Additionally,
must be moved or storage reconfigured to recover			use of storage is made more efficient as very
unused space.			large RAID groups (up to dozens of disks) are now
Within the VA7000, fragmentation of physical			manageable using only two parity disks rather
			than a parity disk for each group of five disks.
space is managed at the RAID (Redundant
Arrays of Inexpensive Disks) block level rather
than in disk-sized chunks. The impact of free-space
management and	“garbage	collection” is

absorbed at the array level, without consuming SAN or server resources.

Technology Trends

Copyright © 2001 by D.H. Brown Associates, Inc.

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