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.

2.1