HP Volume Shadowing for OpenVMS

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Software

Product

Description

PRODUCT NAME: HP Volume Shadowing for OpenVMS

SPD 27.29.21

Note:

This is the Software Product Description (SPD) for the

following three products running on OpenVMS Version

7.2-2, Version 7.3, Version 7.3–1, Version 7.3–2, Ver-

sion 8.2, Version 8.2-1, or Version 8.3:

• HP Volume Shadowing for OpenVMS Alpha

• HP Volume Shadowing for OpenVMS VAX

• HP Volume Shadowing for OpenVMS for Integrity

servers

Except where speciﬁcally noted, the features described

in this SPD apply to all 3 products. The license and

part number information is architecture speciﬁc. Please

refer to the Ordering Information section of this SPD for

further details.

DESCRIPTION

Volume Shadowing for OpenVMS is a System Inte-

grated Product (SIP) that runs on the Integrity server,

Alpha and VAX families of processors. Volume Shad-

owing for OpenVMS implements a RAID Level 1 stor-

age strategy that provides high data availability for disk

devices by preventing data loss resulting from media

deterioration or from controller or device failure. This

strategy also prevents storage subsystem component

failures from interrupting system or application opera-

tions.

Volume shadowing, sometimes referred to as disk mir-

roring, maintains redundant copies of data on a collec-

tion of disk volumes (one copy per disk volume) called a

shadow set. Shadow sets consist of one, two, or three

disk volumes or shadow set members. This duplication

of data provides enhanced data availability; if data is

recorded on multiple disk devices, it remains accessi-

ble if one device becomes unavailable. Disk read and

write operations continue transparently with the remain-

ing members of the shadow set. Note that the terms

disk and device are used in this SPD to refer to a disk

volume.

Because a shadow set is made up of multiple disks

containing the same data, the Volume Shadowing for

OpenVMS software can read data from any full mem-

ber of the shadow set. For each read operation, the

Volume Shadowing for OpenVMS software determines

which disk to read from using an algorithm that maxi-

mizes performance. Volume Shadowing for OpenVMS

ensures that disk write operations are duplicated on all

shadow set members. For maximum performance, Vol-

ume Shadowing for OpenVMS ensures that shadow set

write operations are issued in parallel to full shadow set

members.

If some data on a full shadow set member becomes

unreadable, the shadowing software can read the data

from another available full member. Additionally, with

DIGITAL Storage Architecture (DSA) disks, the mem-

ber with unreadable data can be repaired by the con-

troller by rewriting the data to viable, replacement areas

provided on each disk. Small Computer Systems Inter-

face (SCSI) devices certiﬁed by HP for use with volume

shadowing support data repair. For other SCSI devices,

replacement and repair algorithms are device speciﬁc.

OpenVMS Integrity, Alpha and VAX system disks, Files-

11 On-Disk Structure 2 (ODS-2), and Files-11 On-Disk

Structure 5 (ODS-5) data disks that are certiﬁed by HP

can be volume shadowed. For more information, refer

to the Hardware Requirements section of this SPD.

July 2006

Summary of content (6 pages)

PAGE 1
Software Product Description PRODUCT NAME: SPD 27.29.21 HP Volume Shadowing for OpenVMS Note: This is the Software Product Description (SPD) for the following three products running on OpenVMS Version 7.2-2, Version 7.3, Version 7.3–1, Version 7.3–2, Version 8.2, Version 8.2-1, or Version 8.3: recorded on multiple disk devices, it remains accessible if one device becomes unavailable. Disk read and write operations continue transparently with the remaining members of the shadow set.
PAGE 2
HP Volume Shadowing for OpenVMS SPD 27.29.21 Volume Shadowing for OpenVMS implements a hostbased approach to shadowing disk devices. In previous OpenVMS versions, Volume Shadowing for OpenVMS VAX implemented a controller-based approach to disk shadowing. Controller-based Volume Shadowing for OpenVMS VAX is no longer available or supported.
PAGE 3
HP Volume Shadowing for OpenVMS SPD 27.29.21 The minicopy feature and its enabling technology, write bitmaps, are fully implemented for OpenVMS Alpha and OpenVMS for Integrity servers. OpenVMS VAX V7.3 systems can write to shadow sets which use this feature, but they can neither create master write bitmaps nor manage them with DCL commands.
PAGE 4
HP Volume Shadowing for OpenVMS SPD 27.29.21 HARDWARE REQUIREMENTS • Disks attached to a local VAX SCSI controller on VAX 4000 and VAX 3000 series systems are not supported. Volume Shadowing for OpenVMS does not depend on specific hardware to operate. Basic shadowing functions can be performed on any supported system. Members of a shadow set can be located on any single system or anywhere in an OpenVMS Cluster system.
PAGE 5
HP Volume Shadowing for OpenVMS SPD 27.29.21 A capacity license allows a varying number of disks to be shadowed on a single system, up to the maximum specified in the Configuration Limits section. When using a capacity licensing scheme in an OpenVMS Cluster, every system in an OpenVMS Cluster that mounts a shadow set must have a properly sized Volume Shadowing for OpenVMS capacity license installed.
PAGE 6
HP Volume Shadowing for OpenVMS SPD 27.29.21 The information contained herein is subject to change without notice. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.