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Volume Management: HP 3000 MPE/iX Computer Systems > Chapter 1 Introducing Volume Management
Why Use Volume Management? |
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On many systems all the disk drives are configured as one set, the system volume set. This set contains the system control programs, working space for the system and storage for permanent files. Typically, the files are spread across multiple disk drives. Since system files must be online, and these files are spread across the drives, what happens if any drive goes down? The whole system goes down. Volume management provides a solution to these problems by configuring the drives so that system files are stored together on a separate disk or set of disks. This prevents "nonsystem" disks, containing user data, from affecting the system. If a nonsystem drive goes down, the system continues running. With volume management user data can be grouped on separate disks or sets of disks. This allows systems with removable disks to store specific data offline and easily restore it by mounting a disk pack. Volume management is particularly useful in managing disk storage space for the following reasons:
Volume management attempts to keep as much data as possible available to the system. If all the volumes in the volume set are not mounted, the user is still able to access data from the available volumes in the volumes set. Data can be partitioned into volume classes, so specific volumes can be grouped together to limit access to these volumes. Data can be grouped and stored on specific disks, so that only those disks need to be mounted. If a drive goes offline for any reason, only the users who are currently accessing that drive or volume set of which this drive is a member are affected. Other users can continue normally unless they attempt to access the volume. If the drive comes back online, and there is no damage to the drive, all users can continue after logon. A removable disk may be transported to another disk drive on the current system or another system that has the necessary account structure and processing can continue. In terms of the system volume set, volume management has the ability to add a new drive in critical situations. If in the middle of a large application there is not enough spoolfile space, or not enough permanent disk space, it is not necessary to bring the system down to add a new drive. Assuming that the I/O path had been previously configured, the new drive can be added to the system online, while the application is running. Also, if a new system needs to be installed or a system needs to be rebooted, only the system volume set needs to be available. If the system is configured as one large system volume set, then all files are on that set. If nonsystem volume sets are created, files can be partitioned and assigned to different sets. This allows a volume set to be taken offline when one group of users is finished and another set to be put online for another group of users. Even system volumes can be moved from one drive to another when using the same LDEV. When using removable disk packs, volume sets containing applications needed during the day can be mounted each morning. Large batch jobs that can run overnight could reside on other volume sets, which can be mounted on the same drives in the evening. When using removable disks, sensitive data may be taken offline and placed in a secure location. Special capabilities also protect data on nonsystem volumes. Users without use volumes (UV) capabilities cannot access any files on a nonsystem volume, even if the files are released. Volume management also keeps account security information on the system disk, so there is no possibility of nonsystem or transported disks interfering with the system security structure. |
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