The following is a brief list of the preparation steps.
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 disk files, refer to the
sections "Storing to Disk Files" in this chapter.
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.
Decide on the order that each backup device in the pool is to be
used.
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.
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.
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.
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:
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:
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,*T)
To store files to a set of four parallel devices, you might
use the following set of commands:
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)
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.
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.