Preparing Tape and DDS Devices

Prepare your backup devices by mounting the first media in the stack near each device onto that device. Follow the instructions in Chapter 3, "Preparing Storage Devices," for mounting backup media.

After mounting the media, check the console for a message telling you that the volume has been mounted. For example:

   14:47/31/VOL (Unlabeled) mounted on LDEV#8

Note the backup drive's logical device (LDEV) number. (The LDEV number is 8 in the example above.) You may need it to answer a backup request later.

Single Tape Devices

When you store to a single backup device, STORE only writes files to one device at a time. When the backup media is full, it automatically rewinds then prompts you to load new backup media. When the second unit of backup media is loaded, STORE continues writing files until all of the qualified files are stored or another unit of backup media is needed. If you are storing many files, or files that are particularly large, you may need individually load several units of backup media onto the single device.

Figure 3-7 “Single-Device Backup” illustrates a single-device backup.

Figure 3-7 Single-Device Backup

The FILE command assigns a filename to a backup device according to its logical device number or its device class. For example, the FILE command below assigns the filename T to the device with LDEV 8:

   :FILE T;DEV=8

To store files to only one device, backreference that device in your STORE command. For example:

   :FILE T;DEV=TAPE



   :STORE @.OPERATOR.SYS;*T

Using one or more FILE commands is recommended, especially when your system is configured to automatically allocate devices (autoreply) or when you are using multiple backup devices.




	NOTE: If auto reply is not enabled on the backup device designated, a reply from the console is necessary to allocate that device for a `STORE` process. See Chapter 8, "Handling Media Requests," for more information. If you are using labeled tapes for your backup, you may or may not have to respond to console requests, depending on how your system is configured. Refer to the "Storing to Labeled Tapes" section in Chapter 5 for more information on using labeled tapes.

The FILE command below assigns the filename BACKUP to the device with the device class name TAPE.

   :FILE BACKUP;DEV=TAPE

Using the backup device's logical device number is a more exact way to assign a filename to a particular device. There is only one device defined as LDEV 8 on your system. However, several devices may be assigned the device class TAPE. When you use device classes to name backup devices, STORE asks you to assign a logical device number to each filename with a backup request.

FILE Commands for Automatically Allocated Devices

In order to have devices automatically allocated to the backup, you must assign a different filename for each backup device allocated; use an LDEV number or a unique device class for each FILE command you use, one for each device.

Refer to Chapter 8, "Handling Media Requests," for a description of automatically allocated devices.

Multiple Tape Devices

All STORE and TurboSTORE products allow the use of multiple devices for backup. Multiple devices are identified as a pool of available devices. When you store to multiple devices, the devices must have similar characteristics; different device types are not allowed. The device characteristics that must be identical are:

Devices must be all local or all remote.
All devices must have the same density.
All devices must have the same record size.
All backups must be either labeled or unlabeled; there cannot be a mix.
Different types of backup devices cannot be used together in one backup. A backup must be performed with only one type of backup device at a time. Note that different models of DDS drives (i.e., SCSI or HPIB) can be mixed. Different models of magnetic tape drives (7980, 7980XC, etc.) can also be used together.

Multiple devices can be used as:

Sequential devices.
Parallel devices.
Parallel device pools.

Using Tape Devices Sequentially

With sequential backup devices, when the first backup on the first backup device is filled, it immediately begins writing files to a second backup on the second backup device and the first backup rewinds. When the first backup is rewound, you can unload it and prepare the drive with a new backup. You do not lose time while the first backup is rewinding nor while you are loading a new backup.

When the backup on the last sequential device is filled, the process returns to the first device. It continues cycling through all the devices in the device pool until all of the specified files are stored.

The maximum number of serial magnetic tape or DDS devices allowed is 8. However, you generally do not need to use more than two devices in serial. You get better backup performance if you use multiple devices in parallel. However, using two devices in serial can be useful for some unattended backup functions. For example, if your backup usually fits on one media, then using two devices in serial allows your backup to finish unattended, even if your data grows and one night overflows one piece of media.

Serial devices can also help a backup to continue unattended in the event of a media write error. If STORE encounters an error writing to a backup media, it marks the current media bad and unloads it. It then rewrites the backup data to the next mounted serial device, and the backup continues uninterrupted. This gives you enough time to mount another media on the other drive, if needed.

Figure 3-8 “Sequential Backup” illustrates a sequential device backup.

Figure 3-8 Sequential Backup

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 filenames 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. Instead, 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 three sequential backup devices:

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




	NOTE: Only unlabeled media can be used for a sequential device backup. A maximum of 8 devices can be specified in each serial device pool.

Using Tape Devices in Parallel

With parallel devices, you have the capability of reducing backup time by storing different files on different devices at the same time. When you store files to a set of parallel devices, the files are grouped before the store begins and then copied to multiple devices simultaneously. For example, when you have three parallel devices, your files are partitioned into three subsets. Files in the first subset are copied to the first backup drive, the files in the second subset are copied to the second backup drive, and so on.

When a piece of media is filled, you are prompted to mount the next piece of media on that device.

Depending upon the characteristics of your files and your backup devices, storing files to parallel devices usually saves more time than using sequential devices.

Figure 3-9 “Parallel Backup” illustrates a parallel device backup.

Figure 3-9 Parallel Backup

Currently, all STORE and TurboSTORE products support a maximum of 16 parallel backup devices. The actual speed of performance depends on the system, disk configuration and the backup devices used.

When using a multiple-processor machine, you can see increased backup performance when doing parallel backups. Each parallel device or device pool is controlled by a separate process. Since each process can be run simultaneously on different processors, this will improve your backup performance.

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. This is recommended because STORE uses two additional processes to control the overall backup.




	NOTE: Depending on your system configuration and bandwidth, you should still see increased backup performance using parallel devices, even if you use more parallel devices than you have processors.

To store files to a set of four parallel devices, the following set of commands can be used:

   :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 four parallel backup devices:

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

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

Using Parallel Device Pools

Parallel device pools are multiple sets of sequential devices used in parallel. Using parallel device pools is often the most efficient way to store a large set of files when you have several backup devices. Parallel device pools give you the advantages of both parallel and sequential devices. You copy file subsets to different devices simultaneously, and can have another sequential device ready when the media is filled in any device pool.

Figure 3-10 “Parallel Device Pools” illustrates a parallel device pool backup.

Figure 3-10 Parallel Device Pools

Up to eight serial backup devices are currently supported within a parallel device pool. Maximum performance is obtained by using three or four parallel sets, each consisting of two sequential 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)

Using $NULL as a STORE Device

The devices specified for a backup can also refer to $NULL. This essentially does the backup to the "bit bucket" -- no data is stored to any backup media. This type of backup can be done by specifying a file equation prior to performing the backup. . Instead of specifying a tape device, specify $NULL. For example:

   FILE N=$NULL

Doing so causes STORE to use $NULL as its output device. The command line is parsed, the input fileset scanned, all files are read from disk, and all output is displayed as normal. The only real difference is that the data is not actually being written to an output device.

This feature can be useful when trying to determine which files will be stored by STORE, as a trial run. It can also be used, with EXTREME caution, with the ;PURGE option, to remove all specified files.

When using this feature, keep in mind that your files are NOT being stored to any device, so the data has not been saved anywhere.

Using Remote Devices for Backups

STORE and TurboSTORE now support remote backup devices for storing and restoring files. This feature, which was previously only available using CMSTORE, allows you to specify a backup device, or devices, on a remote system for your backups. A connection to the remote system must exist before the STORE is invoked. Once the remote connection is established, a file equation should be created to point to the remote device. For example, to store to a tape drive on the remote system BROWNY, issue the following FILE command:

   FILE REMOTE;DEV=BROWNY#TAPE

This file equation can then be used as the device file argument to STORE, RESTORE, or VSTORE, or can be used with the STORESET or RESTORESET options. For example, using the file equation defined above, the following STORE command will back up files to a remote tape drive on BROWNY:

   STORE @.@.@;*REMOTE;SHOW

Although the initial console device request will appear on the console of the remote system, all further STORE console messages will be sent to the local system's console. These messages will also be sent to the backup's $STDLIST.




	NOTE: Remote backup is currently only supported for unlabeled backups. Labeled backups cannot be accessed remotely by either `STORE` or `CMSTORE`. Also, magneto-optical devices cannot be used remotely. Any backups to MO devices must be done to a local device.

Preparing Tape and DDS Devices

Technical documentation

» Table of Contents

» Glossary

» Index

Single Tape Devices

FILE Commands for Automatically Allocated Devices

Multiple Tape Devices

Using Tape Devices Sequentially

Using Tape Devices in Parallel

Using Parallel Device Pools

Using $NULL as a STORE Device

Using Remote Devices for Backups