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Using TurboSTORE/iX 7x24 True-Online Backup
When using TurboSTORE/iX 7x24 True-Online Backup, you can perform file,
application, and system backups without closing files or disrupting
users. Some guidelines for performing these backups are discussed below.
TurboSTORE 7x24 True-Online Backup can perform two types of online
backups:
* The first type is referred to as an online backup, which requires
that all files being stored be closed for write access when the
backup first starts. This is the type of online backup formally
available with the TurboSTORE/iX II with Online Backup product.
The online backup refers to a backup created with only the ONLINE
option of TurboSTORE/iX 7x24 True-Online Backup.
* The second type is referred to as a 7x24 true-online backup, which
lets you backup applications without requiring any files to be
closed for write access at any time during the backup.
The 7x24 true-online backup refers to a backup created with the
ONLINE=START or the ONLINE=END option of TurboSTORE/iX 7x24
True-Online Backup.
The Sync Point
When performing a backup, you want to know at what point in time the
backup occurred. This is helpful when performing a recovery so you know
that all files were restored to a state at the same time. This is the
point called the sync point, where all files are synchronized. It can
occur at different times, depending on the type of backup performed.
You can schedule when the sync point occurs (either at the start or the
end) by scheduling when the backup job is launched. Be aware, however,
that a certain set up time is required for TurboSTORE to create the list
of files to be stored. Depending on the number of files being stored,
the sync point may happen soon after the backup is launched, or may occur
5-15 minutes later. To better control when the sync point occurs, a
fixed time can be specified on the STORE command line. See "Creating a
7x24 True-Online Backup (ONLINE)" later in this chapter for more details.
The NOTIFY option can also be used to launch a job stream once the sync
point has occurred. See Chapter 6, "Notification of File Availability
(NOTIFY)".
WARNING All 7x24 true-online backups created with the sync point at the
beginning can be restored on any MPE/iX system. However,
backups created with the sync point at the end can only be
restored or verified on MPE/iX Release 5.5 or later. If you
know at the time you perform the backup that a tape must be
restored onto an earlier release, create the tape with the sync
point at the beginning.
Sync Point at the Beginning of Backup
The sync point is always at the beginning of an online backup when only
the ONLINE option is used. A 7x24 true-online backup can also have the
sync point at the beginning by using the ONLINE=START option.
The main difference between these two types of backups is that an online
backup (ONLINE) requires all files to be closed at the sync point, while
a 7x24 true-online backup (ONLINE=START) allows users to access and
modify their files, uninterrupted, throughout the sync point and backup.
Why Use the Sync Point at the Beginning of a Backup?.
Using the sync point at the beginning of a backup has the following
advantages over using it at the end:
* Synchronizing at the start of a backup gives you better control of
when the sync occurs.
* It spreads the log data throughout the tape and therefore one is
less vulnerable to media errors.
* It allows for faster recovery of partial restores, since sync at
end requires RESTORE to read the log files from the end of the
last piece of media.
* It allows for migration of files to earlier releases of
TurboSTORE/iX, whereas sync at end does not.
For example, scheduling the sync point at the beginning of the backup is
useful when your system is heavily used during the day, making performing
backups then impractical. The backup can be started at the end of the
busy day shift, and run during the night. Since no application shutdown
is required, users, perhaps from other time zones, can continue to access
their files and applications uninterrupted.
Sync Point at the End of Backup
TurboSTORE/iX 7x24 True-Online Backup can also schedule the sync point at
the end of the backup using the ONLINE=END option. Using the options
described in "Creating a 7x24 True-Online Backup (ONLINE)", you can
schedule the sync point to occur at a fixed time, or at the end of the
backup. However, if you specify the sync point to occur at a certain
time, it does not occur until all files have been stored.
Why Use the Sync Point at the End of a Backup?.
Using the sync point at the end of a backup has the following advantages
over using it at the beginning:
* Synchronizing at the end of the backup creates a logically
consistent copy of your data at the time of the end of the backup.
* It gives you the most recent copy of your data.
The backup media can be off the system and stored in a data safe
before running a "risky" application. If the "risky" application
fails, you can recover your data at the point just prior to
starting the application.
* All file changes occurring during the backup are logged and stored
at the end of the backup media.
For example, scheduling the sync point at the end of the backup can be
useful if you start your backup in the middle of the day (at lunch time,
for example). The backup can then run throughout the afternoon shift,
and be finished before your disk-intensive batch jobs are run at night.
Synchronizing at the end would then allow you to save the state of your
system at the end of the working day.
If your batch jobs do not run successfully, you can restore from that
backup without losing a day's work. If this is important to business
operations, you may want to consider backup with the sync point at the
end.