TurboSTORE/iX 7x24 True-Online Backup Options

• Using the ONLINE option only:

  The first type of online backup requires that all files being store be close for write access when the backup first starts. This is the type of online backup available on pre-MPE/iX 5.5 systems, when the TurboSTORE/iX II with Online Backup products are used (product numbers HP36388A or HP36398A). This type of backup is referred to in this manual as an online backup.

• Using the ONLINE=START or ONLINE=END options:

  Using the new functionality of TurboSTORE/iX 7x24 True-Online Backup, you can also do an online backup of files and applications without requiring that files be closed for write access at any time during the backup. This is referred to in this manual as a 7x24 true-online backup.

• The second type of online backup, referred to as a 7x24 true-online backup, lets you backup applications without requiring any files to be closed for write access at any time during the backup.

At the time the online backup is started, all files must be closed for a brief period while they are attached to the shadow logging system. Shadow logging saves the "before images" of file blocks when the records in the file block are modified during online backup. The before images are stored on tape and are used by RESTORE to reconstruct the original contents of the file.

How much time is required for the files to be closed depends upon how many files are being stored. The range of time is usually from 1 to 30 minutes. Applications should be closed during this attach period. Any files open for write access during this period are NOT stored.

The shadow logging subsystem maintains the original state of the files as they appeared when the online backup began. If an attached file is modified, the before image of the portion (block) of the file being modified is saved in a log file. After the store process has written the attached file to the backup media, it requests the logging information from the shadow subsystem and appends the logged data, if any, to the end of the data file.

If an attached file is purged during the online backup, the system logically removes the file, but does not physically remove it until it has been stored. Therefore, the backup reflects the state of the system at the time STORE was initiated.

	NOTE: The shadow logging operation can fail if there is not enough disk space. Error messages are displayed for all files that fail to store due to lack of disk space. However, the backup will NOT abort. You must purchase TurboSTORE/iX 7x24 True-Online Backup (B5152AA) to use the ONLINE option. This functionality is the same as was previously available in TurboSTORE/iX II with Online Backup (HP36388A and HP36398A). Any Image databases being stored with the ONLINE option should be closed for write access before the backup is started. If user logging is enabled for the database(s), then the current log file should be closed when the database is closed. Once the attach period has finished, the database can be opened again. A new user log file should be started at this time.

Heavily modified files should be stored first. This is accomplished by specifying these files first in the STORE command fileset list. By storing these files first, you reduce the system overhead and the amount of logging information written to the backup media.

When online backup begins, the shadow subsystem assigns each file in the store fileset to a log file created on the same volume where the file resides. Actual logging activity does not take place unless the file is modified after the attach phase.

TurboSTORE saves the changes made to databases and files being stored in special log files. These files can become quite large when there is a lot of activity on the system. The LOGVOLSET option allows you to specify which volume set to use for the log files. You can use this feature with the log file size summary statistics from previous backups to ensure that there is enough disk space for the online backup log files. The log volume set is specified as follows:

   :STORE /;*tape;ONLINE;LOGVOLSET=volumeset

The amount of log space required is directly proportional to the amount of modifications performed against the attached file. Therefore, the more modifications made to an attached file, the more log space required. In the worst case, the maximum amount of log space required equals the sum of the space required for all of the files being stored. By storing the heavily modified files first, you reduce the amount of logging space required. Reducing the amount of logging data written to the backup media will also reduce the time required to restore the files.

As each piece of backup media is filled, logging is disabled for the files that were stored on that media.

Use the ONLINE parameter of STORE to perform an online backup. Before the STORE process is initiated, you must warn the users to close all files to ensure that the files are both physically and logically consistent. For example, the following message can be sent:

   WARN @S;ONLINE BACKUP WILL BEGIN IN TEN MINUTES.

   WARN @S;PLEASE CLOSE YOUR FILES.

Begin the online backup by specifying the ONLINE parameter with the STORE command. For example, the following illustrates the STORE command for an online backup.

   :STORE @.@.@;*T;DIRECTORY;ONVS=MPEXL_SYSTEM_VOLUME_SET,NV1;ONLINE

The following illustrates the STORE command entry for an online backup to a magneto-optical device.

   :STORE @.@.@;;MOSET=(101);NAME=DAILY.D24SEPT.TIGER;DIRECTORY;&

   ONVS=MPEXL_SYSTEM_VOLUME_SET,NV1;ONLINE

When online backup begins, all files not currently open for write are attached to a log handler known as the shadow subsystem. Once the attach phase is complete, STORE issues the following message to the console.

FILES LOCKED BY ONLINE STORE ARE NOW FREE FOR READ/WRITE/PURGE

This message is also written to $STDLIST if STORE is being run from a session. After you receive the above message, the users are allowed read, write and purge access to the attached files. Send your users a message telling them they may resume their applications. For example:

   WARN @S;ONLINE BACKUP HAS BEGUN.

   YOU MAY NOW RESUME YOUR APPLICATIONS.

The NOTIFY option (described earlier in this chapter) can be used to automate this task.

If any files were still open at the time you started online backup, you will receive the following message:

 

   ! NOT STORED:  FILE OPEN FOR WRITE AT ATTACH 

where the exclamation point ( ! ) is replaced by the actual filename(s).

During the RESTORE process, the log file is used to reconstruct the original contents of the files; that is, the way they appeared at the moment they were attached during online backup.

	NOTE: The ONLINE option cannot be specified with the SPLITVS or TRANSPORT options.