OpenVMS RAM Disk, Cache, and Disk Striping

Overview: Virtuoso

The Virtuoso Components Flow Diagram
Figure 1: The Virtuoso
Components Flow Diagram

The software offers virtual-disk capabilities on OpenVMS systems. A virtual disk appears at the application level as an actual device. Which in reality is a software-maintained and software-generated representation of a logical device, using an area of memory and/or a real drive to do the following:

  • Reduce the amount of I/O and improve overall-system performance and throughput
  • Provide better resource utilization of logical drives
  • Achieve improved management and operational effectiveness of logical drives
  • Significantly increase the security of data sensitive and/or critical files

The Virtuoso software supports two types of virtual disks---memory-based and drive-based. Each has its own advantages. By using our software you can tune the attributes of each to achieve the optimum configuration for your needs. Memory-based procedure uses an area of physical or paged memory as its working space and treats this area, as if it were an actual drive. This type is the fastest, since I/O requests are satisfied, using high-speed memory. Through use of the writeback interval you can cause all modified pages of an active memory-based drive to be written to a backing store. The writeback interval enables you to specify in seconds, when modified pages are written back to their backing store. The interval determines, whether the writeback is immediate (write through) or periodic. This ensures that the contents of the virtual memory area in case of a system failure or reboot is saved.

The system provides two kinds of memory-based options---paged memory and physical (non-paged) memory. Paged-memory allows mapping to a private section that serves as its backing-store file. Since a VMS process handles the I/O requests, tuning its working set determines how much of the disk is cached in memory. If your systems are limited by physical memory or have a requirement for large drive, you will find this feature helpful.

Physical memory drives use portions of non-paged memory as their work area. Thus, all blocks of the disk are always in memory. If your systems are not limited by physical memory, this feature will prove useful to you.

A backing store is the nonvolatile representation of a virtual disk's contents. Memory-based must use a local file as its backing store. Disk-based virtuals can use local files (contiguous or noncontiguous), whole or partial volumes, and networked files or volumes.

The system supports three kinds of drive-based virtual disks---file, volume, and network. File represents a local virtual disk residing in one or more files. The file can be contiguous or noncontiguous. Volume represents a virtual disk residing in one or more partial or complete, physical volumes. Network represents a virtual disk residing in one or more files or volumes on a remote DECnet node.

Our software can increase the speed of a drive-based virtual disk three ways:

  • By caching all or a portion
  • By using the Virtuoso Disk-Striping facility
  • By specifying contiguous files

It supports all standard OpenVMS QIO functions, normally associated with logical drives. It allows you to Access, Activate, Deactivate, Modify, Monitor, and List virtual drives with specific configurations, sizes, and characteristics.

Virtuoso uses standard-DCL syntax, as well as the normal OpenVMS privileges required for manipulating volumes.


Caching consists of saving copies of the most frequently accessed sectors in memory. This increases the effective-transfer rate between your application and the requested data. Using dynamic caching, the software can automatically extend and/or reduce the size of the cache, based upon the physical-memory constraints. Static caching is also available.

In addition caching priorities can be established. Simply instruct Virtuoso to skew its cache in favor of the device's list of cached files.

Disk striping consists of interleaving the contents of a virtual disk over multiple backing stores. Interleaving is the alternating use of multiple sectors (usually one track) on two or more backing stores. Logically, a single drive appears, even though you use multiple backing stores. Striping helps to prevent the throughput of a single drive from becoming a bottleneck. By spreading I/O's across multiple drives, you can use several data paths and heads simultaneously. This limits disk queuing and improves I/O response time.

To protect your files from intrusion, a Security option is provided. This option allows you to select a group of users who, depending on VMS job type, may be able to issue a read and/or write operation. Each user or job type may also be required to authenticate themselves prior to accessing the virtual disk. The Security facility also provides an Encryption option for data sensitive information. Encryption is a process of jumbling or encoding data before it is stored in files. The information appears illegible to anyone who tries to decipher its meaning without providing the correct encryption key. When you specify this option at activation time, the software prompts you for a key to use for encrypting and decrypting the data. Virtuoso then encrypts all data, stored in virtual devices.

To gain subsequent access to your encrypted data, you must supply the correct encryption key.

Virtuoso supports the use of Networked Virtual Drives, having a backing store located on a remote node. The backing store can be a file or a volume. It also supports a data-compression feature that can significantly reduce the amount of network data that is transmitted and/or received. For sensitive data, Network Data Encryption is also available.

The Hardware Error Simulation facility can return specific classes of error information within designated blocks of data to test your recovery procedures, allowing the ability to simulate three types of errors. These are parity errors on the basis of logical-block numbers, device-write-lock errors, and device-offline errors.

Analysis Tools

The Device Statistics Collector records specified classes of historical statistics in a log file. These include caching, device, file, and file-control data.

Later, the Report facility selects the raw data from the data-collection file, formats it, calculates it, and uses it to produce a report. Moreover, you can inquire about the characteristics of a collection in progress. These include the classes of data to collect, the beginning and ending times, the sample-interval times, and the specs for each device.

To create a report, you can take all or only a part of the information, the Device Statistics Collector has previously logged into the collection file. Thus, you can report upon whichever class(es) of information you choose.

Virtuoso Monitor provides a window into the activity of a particular virtual drive or a summary window on a subset of active drives. The program performs three major tasks. It displays a full status of all disk sets for a given node on any DEC-supported terminal. It controls the size, location, and the order of the windows. It performs Add, All, Advance, Backup, Move, Paste, Print, Refresh, Remove, Set, Top, and Unpaste operations. Thus, you can examine all or part of the current activity.

The different classes of statistics you can monitor with the Monitor program are caching, cluster, I/O, and striping data. Monitor also allows you to issue most commands---Access, Activate, Modify, and Deactivate---as well as Spawn and Help commands from the Monitor prompt.

Minimum Hardware Supported

The Virtuoso software runs under the OpenVMS operating system under all standard, VAX and Alpha hardware configurations. Virtual disks require that the drives used as backing stores be OpenVMS-compatible. Virtuoso fully supports the VMScluster environment.

Prerequisite Software

Virtuoso V1.5 operates on any OpenVMS processor, using OpenVMS VAX Version 5.5-2 or later, or OpenVMS Version 6.1 or later.

Optional Software

  • SHADOW for OpenVMS Mirroring System
  • File SHADOW Option for File Shadowing
  • RemoteSHADOW Option for Intra-Day Business Recovery

Software Installation

Installation of this product is subject to the terms of the ASCI Standard Software Product License Agreement. The software is designed to be Customer installable and uses Compaq's VMSINSTAL facility.

Warranty Information

This software is sold through ASCI's Software Product License Agreement which warrants the product for ninety (90) days from the date of purchase. Warranty services include telephone-remedial support and product upgrades. Additional maintenance services after the warranty period---as well as consulting or product training---are available and are separately priced.

Maintenance Information

After the initial product warranty expires, ASCI offers a twelve-month maintenance plan. This includes telephone-remedial support, product upgrades, and enhancements, as they become available. The annual maintenance plan is separately priced.

Ordering Information

ASCI distributes all material via the web. Current prices are available upon request. Multi- CPU and Educational Institutions discounts are available.

Virtuoso is licensed under HP's License Management Facility (LMF). A Product Authorization Key (PAK) is required prior to product installation and execution.

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