Software Product Description ________________________________________________________________ PRODUCT NAME: VMS Volume Shadowing, Version 5.4 SPD 27.29.07 DESCRIPTION VMS Volume Shadowing is a System Integrated Product (SIP) avail- able on VMS systems. VMS Volume Shadowing provides high data availability by ensuring against data loss resulting from me- dia deterioration or through controller or device failure. This prevents storage subsystem component failures from interrupting system or application operation. Volume shadowing maintains multiple redundant copies of data on a collection of disks called a shadow set. Shadow sets consist of one, two, or three compatible disk volumes which are referred to as shadow set members. This duplication of data provides greater data availability. When data is recorded on more than one disk volume, the data is accessible even when one volume is unavailable. Disk input/output operations continue transparently with the remaining members of the shadow set. Because a shadow set is made up of multiple disks containing the same data, the VMS Volume Shadowing software can read from either disk device. The VMS Volume Shadowing software determines which disk to read from, per read operation. If sections of a volume become unreadable, systems with volume shadowing can read the data from the duplicate and attempt to repair the original by writing the data to good blocks. VMS system disks and any Files-11 On-Disk Structure 2 (ODS2) data disks can be volume shadowed. DIGITAL September 1990 AE-HP37H-TE VMS Volume Shadowing, Version 5.4 SPD 27.29.07 For the purposes of this document, the term CPU is used to refer to a single VAX computer. A CPU may be standalone or a member of a VAXcluster. VMS Volume Shadowing provides two modes of performing shadowing operations on the VMS Operating System: o VAX Volume Shadowing Phase I This is the original implementation of the VAX Volume Shad- owing product. Phase I VMS Volume Shadowing provides for centralized shadowing on VMS systems using Hierarchical Stor- age Controllers (HSC). This mode of shadowing is limited to disks connected to HSCs, either in a VAXcluster or single CPU. o VMS Volume Shadowing Phase II Phase II allows shadowing on the same configurations as Phase I plus it supports VAXcluster wide shadowing of disks on a single CPU or located anywhere in a VAXcluster system. VMS Volume Shadowing Phase II supports VAXcluster wide shad- owing of all Digital Storage Architecture (DSA) devices. Phase II is not limited to HSC-controlled disks, but extends volume shadowing capabilities to all DSA disks including those on local adapters, all Digital Small Systems Interco- nenct (the DSSI RF series) disk devices on any VAX computer, and VMS MSCP served disks located anywhere in any supported VAXcluster configuration. It is possible to use both modes of shadowing on the same CPU or VAXcluster system at the same time. Any given shadow set must be either Phase I or Phase II; a shadow set cannot be a mixture of the two modes of shadowing. Characteristics CPUs and Controllers 2 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 VMS Volume Shadowing requires a minimum of one VAX CPU, one MSCP- compliant mass storage controller, and one Digital Storage Architecture (DSA) disk drive and volume. Although only one disk is required, there must be two or more disk drives and volumes in order to "shadow" or maintain multiple copies of the same data. This configuration provides protection against either failure of a single disk drive or deterioration of a single volume. Using two controllers provides a further guarantee of data availability in the event of a single controller failure. Using a VAXcluster and multiple controllers provides the greatest data availability. Shadow Set Membership A shadow set can have one, two, or three members. The ability to have a shadow set with only a single member allows a two- member shadow set to continue operation after the failure of one member. It also allows a second member to be added at any time with no disruption of the application. All members of a shadow set must be of the same disk type, for example, all RA90s or RF31s. See the Supported Hardware Devices section for a list of those disk devices supported in shadow sets. Transparency to the End User The shadow set acts as a single disk. The user makes no effort to have the data propagated to all of the members of a shadow set. It is a task of the volume shadowing software to replicate the data on all shadow set members. VMS Volume Shadowing is invisible to application programs and users. All commands and program language features that address data on non-shadowed disks may be used to address data on shad- owed disks with no changes. 3 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 Individual disks may be added to or removed from the shadow set without affecting either the end user or any application. Shadow Set Operation A disk can be removed from the shadow set by operator command or automatically. A failed disk is removed from the shadow set automatically; no operator intervention is required. A disk is only added to the shadow set on command. Within a reasonable period of time, the newly added shadow set member is made identical to the other member(s). Full read/write access to the shadow set continues while the new member is being added. System Disk Shadow Sets System disk(s), like any other Files-11 ODS2 disks, can be shadowed. Restrictions A quorum disk cannot be shadowed in a VAXcluster system. Disks cannot have hardware write protection enabled. Hardware write protection stops volume shadowing software from maintain- ing identical volumes. In a VAXcluster with more than one Star Coupler, Phase I shadow- ing is limited by the following restrictions: o If a VAX is to directly access a Phase I shadow set on an HSC, the VAX must have a direct CI path to that HSC (be connected to the same Star Coupler). o Phase I shadow sets may be MSCP served over the CI. To do this, the VAXs must be on the same Star Coupler as the HSC(s) with the shadow set. These VAXs can then MSCP serve the shadow set to other VAXs connected to other Star Couplers. If a VAX is accessing a Phase I shadow set via another VAX's MSCP Server, it cannot directly access any Phase I shadow set on any local HSC. Essentially, a CPU must access all its 4 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 Phase I shadow sets either locally or via a served path. It cannot do both. o VAXs accessing Phase I shadow sets via an MSCP served path (over the CI or Ethernet) cannot add or remove members of the shadow set, they have data access only. o Phase II shadow sets are not subject to any of the above restrictions involving multiple star couplers. Phase I supports a maximum of 16 shadowed disks per HSC or HSC pair (for dual pathed disks). Phase I supports a maximum of 8 shadow sets per HSC or HSC pair (for dual pathed disks). For additional information about restrictions, refer to the VMS Operating System Software Product Description (SPD 25.01.xx) and the VAXcluster Software Product Description (SPD 29.78.xx). HARDWARE REQUIREMENTS - PHASE I Refer to the VMS Operating System Software Product Description (SPD 25.01.xx) and VAXcluster Software Product Description (SPD 29.78.xx) for information about hardware requirements and supported CPUs. At least one HSC series controller is required. Shadow sets must be made of identical types of disks (for exam- ple, all RA90s) connected to the same HSC. If the disks are dual pathed between two HSCs, all members of the shadow set must be dual pathed between the same pair of HSCs, and both HSCs must be connected to the same Star Coupler. 5 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 HARDWARE REQUIREMENTS - PHASE II VMS Volume Shadowing Phase II does not depend on specific hard- ware in order to operate. All shadowing functions can be per- formed on any supported VAX CPU by the VMS Operating System. Shadowing capabilities are supported on all disks and con- trollers listed in the Supported Hardware Devices section of this SPD. All members of a shadow set must be the same type of disk (for example, all RA90s or all RF71s). Members of a shadow set may be located on a single CPU or anywhere in a VAXcluster. There are no requirements on the location of shadow set members beyond the valid disk configurations defined in the VMS Operating System Software Product Description (SPD 25.01.xx) and VAXcluster Software Product Description (SPD 29.78.xx). Supported Hardware Devices VMS Volume Shadowing supports the following devices and con- trollers for both Phase I and Phase II shadowing, unless other- wise specified. These devices may be components of Storage Array (SAxxx) products. Disk Controllers and Adaptors All HSCs supported by the VMS Operating System Controllers Supported by Phase II Shadowing Only: o KDA50 o KDB50 o KDM70 o KFQSA o RQDX3 o RQDX2 6 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 o UDA50 Disks Supported by Volume Shadowing: o RA60 o RA70 o RA80 o RA81 o RA82 o RA90 o RA92 o ESE20 o RF30 (Phase II only) o RF31 (Phase II only) o RF71 (Phase II only) o RD51 when connected to RQDX controller (Phase II only) o RD52 when connected to RQDX controller (Phase II only) o RD53 when connected to RQDX controller (Phase II only) o RD54 when connected to RQDX controller (Phase II only) CLUSTER ENVIRONMENT PHASE I and PHASE II VMS Volume Shadowing is fully supported when installed on any valid and licensed VAXcluster configuration without restric- tions. The HARDWARE REQUIREMENTS section of this product's Software Product Description and the VMS Operating System 7 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 Software Product Description (SPD 25.01.xx) list any special hardware required by this product. VAXcluster configurations are fully described in the VAXcluster Software Product Description (SPD 29.78.xx). If VMS V5.3 and V5.4 are both present in a VAXcluster, members of the VAXcluster that are running VMS V5.3 can only access Phase I shadow sets. Members of the VAXcluster running VMS V5.4 can access either Phase I or Phase II shadow sets. SOFTWARE REQUIREMENTS PHASE I and PHASE II o VMS Operating System V5.4 o HSC Software V3.9 Refer to the VAXcluster Software Product Description (SPD 29.78.xx) for information about rolling upgrade restrictions. VMS Tailoring PHASE I and PHASE II For VMS V5.x, the following VMS class is required for full functionality of this layered product. o VMS Required Saveset For more information about VMS classes and tailoring, refer to the VMS Operating System Software Product Description (SPD 25.01.xx). OPTIONAL SOFTWARE None 8 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 GROWTH CONSIDERATIONS The minimum hardware/software requirements for any future ver- sion of this product may be different from the requirements for the current version. ORDERING INFORMATION Software Licenses: QL-AB2A*-** Software Documentation: QA-AB2AA-GZ Software Product Services: QT-AB2A*-** * Denotes variant fields. For additional information on avail- able licenses, services and media, refer to the appropriate price book. The above information is valid at the time of release. Please contact your local Digital office for the most up-to-date infor- mation. SOFTWARE LICENSING This software is furnished under the licensing provisions of Digital Equipment Corporation's Standard Terms and Conditions. For more information about Digital's licensing terms and poli- cies, contact your local Digital office. LICENSE MANAGEMENT FACILITY VMS Volume Shadowing supports the VMS License Management Facil- ity ( LMF). License units for this product are allocated on a CPU-capacity basis. Every CPU in a VAXcluster that mounts a shadow set must have a VMS Volume Shadowing License installed. 9 VMS Volume Shadowing, Version 5.4 SPD 27.29.07 For more information about the License Management Facility, refer to the VMS Operating System Software Product Description (SPD 25.01.xx) or the License Management Utility Manual of the VMS Operating System documentation set. For more information about Digital's licensing terms and poli- cies, contact your local Digital office. SOFTWARE PRODUCT SERVICES A variety of service options are available from Digital. For more information, contact your local Digital office. SOFTWARE WARRANTY Warranty for this software product is provided by Digital with the purchase of a license for the product as defined in the Software Warranty Addendum of this SPD. [TM] The DIGITAL Logo, HSC, RA, RD, VAX, VAXcluster and VMS are trademarks of Digital Equipment Corporation. 10