Preparation Process

1. You must first determine what type of device(s) to use for your backup. Most of this section deals with storing to magnetic tape or DDS devices. These procedures can also be followed if you are using a StorageTek device. If you want to use MO media or disk files, refer to the sections "Preparing MO Disks" and "Storing to Disk Files" in this chapter.

2. If you are using tape or DDS devices, you must next decide if you will use a single device or multiple devices. All versions of STORE and TurboSTORE can store to multiple devices. The possible configurations available are:

   Single

   Requires only one backup device. When the media (tape or DDS) fills, the device rewinds the media, you remove the media and replace it with new media, and additional files are stored to the new media.

   Sequential

   Requires more than one backup device. One device is used at a time. When the media (tape or DDS) fills, additional files are stored on the next device in line. You can set this up to toggle between two devices, giving you time to change media.

   Parallel

   Requires more than one backup device. Files are being stored to more than one device at the same time. When the media is full on one device, you remove the media and replace it with new media, and additional files are stored to the new media.

   Parallel Pools

   Requires more than two backup devices. Files are being stored to more than one device at the same time. This is a combination of Sequential and Parallel. When the media (tape or DDS) fills, additional files are stored on the next device in line. You can set this up to have multiple pairs of toggling devices.

3. Decide on the order that each backup device in the pool is to be used.

4. Assign each device a position in the backup, identifying each device by its logical device (LDEV) number. Use the chart in Figure 3-1 “Multiple-Device Planning Chart” as a tool to help you assign your device. Sequential devices are numbered 1 through 8. Parallel devices are identified by the letters A through P.

   Write the LDEV numbers in the order and configuration that you plan to do the backups. Note that the chart for parallel device pools shows only two sequential devices in each parallel set. If you are using your devices in a different parallel pool configuration, you should create your own chart and identify the position of each LDEV.

Figure 3-1 Multiple-Device Planning Chart

Selecting the Backup Method

The best way to use your backup devices depends upon the characteristics of the files that you are storing, your needs for compatibility with other versions of MPE, and your system configuration.

The characteristics of the set of files help determine choices (or options) for storing them. Generally speaking, the more files being stored, the more it is to your advantage to use multiple devices. If you are storing only a few files of moderate size, one backup device may be sufficient. If you are storing many files (for example, all the files in an account, or a smaller number of very large files), using a multiple-device backup is probably to your advantage.

Your needs for compatibility with other versions of MPE limit your choices. If you need to produce STORE backups that are compatible with MPE V/E using the TRANSPORT parameter, you can only store files to a single device.

If you are not creating tapes for use by MPE/V, then your system configuration is the most important determinant of which multiple-device backup method to use. Use the following guidelines to select a method:

Which and How Many Backup Devices Do You Have?

Which devices you may use for a multiple-device backup are described in this chapter. Obviously, to use sequential or parallel devices, you must have at least two backup devices. If you have two or three devices, you may use either parallel or sequential devices. If you have three or more devices, you may use two or more parallel device pools.

If you want to use magneto-optical devices or disk files, refer to the sections "Preparing Magneto-Optical (MO) Disks" and "Storing to Disk Files" later in this chapter. If you are using StorageTek devices, most of the guidelines for tape and DDS devices will apply.

If you are using StorageTek devices, you should follow the directions for tape and DDS devices. However, note that due to the higher throughput of these devices, they should be configured on your system for maximum performance. Refer to the Configuration Guide (put real name there) for information on the proper configuration for 3480 devices.

Selecting Backup Device Order

Once you have determined how many devices you are going to use for your backup, you should determine the order of each device in the backup. Assign each device a position based on its logical device (LDEV) number.

Use the chart in Figure 3-1 “Multiple-Device Planning Chart” to help you assign your devices. Select one of the methods in the chart, and then write in the LDEV numbers of each device you plan to use in the order that you plan to use it. For example, if you intend to use two parallel devices, write in the LDEV number of the first device next to Device A and the LDEV number of the second device next to Device B in the Parallel section of the chart. It may be helpful for you to photocopy the chart and use it as a guide whenever you use a multiple-device method to store files.

Assigning Device File Names

When using multiple backup devices, you have the choice of entering multiple FILE commands to assign a different filename to each device or a single FILE command.

Assigning each device a different filename makes it easier to keep track of each device's position in the backup media. When you receive media requests, you know exactly to which device the request applies. You may use LDEV numbers or a common device class in the FILE command. When you use a device class to name backup devices, STORE asks you to assign a logical device to the filename with a media request. Refer to Chapter 8, "Handling Media Requests" for more information. You must use LDEV numbers to name devices if the devices are to be automatically allocated.

Assign unique filenames based on each device's position in the backup. For example, if you plan to use four parallel devices, you might issue the following set of FILE commands:

   :FILE BACKA;DEV=7

   :FILE BACKB;DEV=8

   :FILE BACKC;DEV=9

   :FILE BACKD;DEV=11

Label sequential devices in order. For example, if you are using three sequential devices, you might issue the following FILE commands:

   :FILE BACK1;DEV=TAPE

   :FILE BACK2;DEV=TAPE

   :FILE BACK3;DEV=TAPE

Label parallel device pools both in parallel and sequential order. For example:

   :FILE BACKA1;DEV=7

   :FILE BACKA2;DEV=8

   :FILE BACKB1;DEV=9

   :FILE BACKB2;DEV=11

If you issue a single FILE command when using multiple backup devices, you assign a common filename and common device class to all of your backup devices. For example:

   :FILE T;DEV=TAPE

You use the common filename, T in the example above, to refer to each device in your STORE command. In a media request, the system asks you to assign an LDEV number to T for each device. If you have four backup devices, you see four identical media requests. You assign a different LDEV number to each media request based upon the order in which you receive the requests. Refer to Chapter 8, "Handling Media Requests," for more information.

Your FILE command gives the backup device a filename and identifies the device. To store files to only one device, you backreference that device in your STORE command, as described previously. For example:

   :FILE T;DEV=TAPE

   :STORE @.OPERATOR.SYS;*T

However, you may choose to employ multiple device configurations at times when you have a large set of files to store and you want to speed up the process. If so, you probably want to use the FILE command to give each device a filename that reminds you of its position. Then use the STORESET parameter in a STORE command to reference the multiple devices. For example, to store files to three sequential devices, use the following set of commands:

   :FILE SEQ1;DEV=7

   :FILE SEQ2;DEV=8

   :FILE SEQ3;DEV=9

   :STORE @.@.@;;STORESET=(*SEQ1,*SEQ2,*SEQ3)

The above STORE command copies all system and user files to three sequential devices. The parentheses surrounding backreferenced file names group the devices into a device pool.

	NOTE: You do not backreference the filename of a backup device immediately after the name(s) of the file(s) you are storing when you use the STORESET parameter. Rather, you must use a placeholder for the missing parameter normally supplied when using a single backup device. The placeholder is provided by the use of ;; in the STORE command.

If you gave the backup devices a single filename such as:

   :FILE T;DEV=TAPE

enter the following STORE command to copy files to a set of four sequential backup devices:

   :STORE @.@.@;;STORESET=(*T,*T,*T)

To store files to a set of four parallel devices, you might use the following set of commands:

   :FILE PARA;DEV=7

   :FILE PARB;DEV=8

   :FILE PARC;DEV=9

   :FILE PARD;DEV=11

   :STORE @.OPERATOR.SYS;;&

   :STORESET=(*PARA),(*PARB),(*PARC),(*PARD)

If you gave the backup devices a single filename such as:

   :FILE T;DEV=TAPE

enter the following STORE command to copy files to a set of three parallel backup devices:

   :STORE @.@.@;;STORESET=(*T),(*T),(*T),(*T)

You describe parallel devices in the STORESET parameter by enclosing each backreferenced device filename within parentheses. Use commas to separate devices.

To store files to parallel device pools, use parentheses to group the devices into pools. Separate the devices in the pool from one another with commas. Commas also separate each device pool. For example, the following commands copy files to two parallel device pools. Each device pool contains two sequential devices. In the following example, STORE uses a total of four devices divided into two device pools.

   :FILE PPA1;DEV=7

   :FILE PPA2;DEV=8

   :FILE PPB1;DEV=9

   :FILE PPB2;DEV=11

   :STORE @.OPERATOR.SYS;;STORESET=(*PPA1,*PPA2),(*PPB1,*PPB2)

If you gave the backup devices a single filename such as:

   :FILE T;DEV=TAPE

enter the following STORE command to copy files to a set of parallel device pools:

   :STORE @.@.@;;STORESET=(*T,*T),(*T,*T)

	NOTE: Up to 16 parallel devices may be specified for one backup. With a serial device pool, up to 8 devices may be specified. When using a multiple-processor machine, you can see increased backup performance when doing parallel backups, since each parallel device gets its own process. A general rule for doing multi-processor parallel backups is to use one less parallel set than you have processors. For example, on a 4-way system, perform a 3-device parallel backup.