The Benefits of ISP

When creating a volume in VERITAS Volume Manager in previous releases, you could specify the disk storage on which to lay out its various parts, subdisks, plexes, and so on. In specifying the storage to be used, you had to take into account the tolerance of a volume to failure of any component of the storage infrastructure, and how the specified layout affected I/O performance and reliability of service. For small installations with a few tens of disks in relatively low-specification arrays, you could either specify the storage layout manually to commands such as vxassist, or rely on vxassist to choose appropriate storage based on general layout specification, such as "mirror across controllers" and "mirror across enclosures," and using the set of heuristic rules that are hard-coded within vxassist.

The traditional model for allocating storage to volumes is shown in Traditional Model for Creating and Administering Volumes in VERITAS Volume Manager. This illustrates that, although some storage attributes are known to VxVM, you must do most of the work in deciding how to lay out the storage if you are to create a volume with the desired performance, reliability and fault tolerance.

Traditional Model for Creating and Administering Volumes in VERITAS Volume Manager

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When intelligent disk arrays are used, many sophisticated features, such as RAID capabilities, snapshot facilities, and remote replication, are provided by logical unit storage devices, LUNs, that are exported by the disk array. Such devices may or may not have ways of making their attributes known to VxVM. In any case, you may be presented with hundreds or thousands of LUNs connected over a SAN.

Allocating storage to volumes when faced with a potentially large number of devices with widely varying and possibly hidden properties is a daunting task to perform manually. ISP aids you in managing large sets of storage by providing an allocation engine that chooses which storage to use based on the capabilities that you specify for the volumes to be created.

How ISP Enhances Volume Management illustrates how ISP improves on the traditional model for creating volumes. The main differences are that the set of information about the available storage is potentially unlimited, and the set of rules that the allocation engine uses to choose storage is defined externally to commands such as vxvoladm.

How ISP Enhances Volume Management

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Summary of the Benefits of Using ISP

The following list summarizes the main benefits that VERITAS ISP provides over the existing storage allocation features in vxassist:

• Storage is automatically allocated based on abstract requirements such as the desired capabilities of a volume.
• Prefabricated capabilities that are provided by vendor-specific features of intelligent storage arrays can be encoded as storage attributes, and used to allocate storage.
• Volumes can be created or grown in batch mode safe in the knowledge that ISP will balance the requirements of all volumes.
• All ISP operations preserve the original intent of the volumes. There is no possibility that operations such as grow, evacuate, add mirror, or add column can accidentally degrade the reliability or performance capabilities of a volume.
• ISP is SAN-aware and understands SAN attributes. It is also capable of using VAIL to learn the capabilities of LUNs.
• The annotation service, provided in the VEA graphical user interface, allows you to define attributes for LUNs that lie outside their discovered hardware characteristics, and to assign values to these attributes.

Limitations of ISP

The following features of vxassist are not currently supported in ISP:

• The vxassist utility includes a number of hard-coded rules that it uses when selecting storage. For example, vxassist may configure objects on separate controllers without being instructed to do so. ISP requires that the selection of storage is made explicit through rules, capabilities and templates.
• ISP supports space-optimized instant snapshots and full-sized instant snapshots that are created on pre-prepared volumes. It does not support third-mirror break-off snapshots.
• Disk group split and join is supported at the level of storage pools. A snapshot of an application volume should be created within a clone pool if it is to be moved between disk groups.
• Templates are not provided in the base product to support the special features of EMC Symmetrix arrays.