Continuous data protection (Backup set option)
Creation Date: July 31, 2006
Revision Date: October 11, 2018
Product: DS‑Client
Introduction
Users often want to protect ongoing changes to their data as soon as the changes have occurred. Examples of such data are word processing or spreadsheet files and the Contacts, Calendar, Notes, and Drafts in a mailbox.
Weekly or daily scheduled backups are not sufficient to prevent data loss caused by unexpected failures on the data source. Though more robust as a backup strategy, hourly backups can consume too much system resources when a complete file system or mail server scan is required.
Continuous Data Protection (CDP) is a backup solution that continuously monitors the changes on a target server and backs up ongoing changes as soon as the changes are detected. It retains intermediate changes so that users can recover images from a specific time. Continuous data protection differs from a “point-in-time” backup and from replication or mirroring, which only keeps a snapshot of the latest image.
After a CDP backup begins (on demand or as scheduled), the session will continue to run unless explicitly stopped, for example, by the scheduled end time or by the user. DS-Client continuously monitors the ongoing changes on the target backup server throughout the entire backup session. As soon as DS-Client detects a change, it immediately backs up the changes to DS-System.
See also:
Recommendations for configuring backup sets with CDP
When you configure a File system backup set with CDP, it is not necessary to select an entire server to back up. Like typical File system backup sets, you can select specific parts of a server, including any combination of share level, directory level, and file level filters. Extended regular expressions can be used to define complex selections.
When you configure a Microsoft Exchange Server backup set (EWS) with CDP, you can select user accounts, or individuals folders (such as Inbox, Sent, Contacts, Calendar, Notes) within user accounts, for backup.
Selecting individual email messages in a backup set with CDP is allowed but not recommended. When an individually selected email message is removed from its original location, it will not be backed up.
DS-Client can also be configured with Local Storage for faster recovery.
The Retention feature can help you to manage the number of online generations stored on DS-System. For more information, see
“Working with retention rules”.
Features and limitations
• Use Buffer and Pre-Scan are unavailable when CDP is used.
• A regular backup process stops after all the backup items have been processed. Once started (by schedule / on demand), the CDP process will not stop until one of the following events:
• An on-demand stop is issued (i.e. click “Stop”).
• The scheduled time limit is reached.
• It runs out of retry connect times to DS-System (including restart backup scenarios).
• Some other unexpected stop condition (Exceptions, failed to connect to target, etc.).
• Windows support with CDP:
• Follow Junction Point is NOT supported because DS‑Client cannot be notified of changes that happen inside a junction point.
• Backup data in Remote Storage is supported. However, like normal backup, if the data on the remote storage is changed but not the placeholder, DS‑Client cannot detect the change.
• Backup Single Instance Store file data is supported.
• If you migrate a backup set in which CDP is enabled, the same limitations apply to the new target server.
• You can enable CDP in a backup set in which CDP has not been enabled as long as all the conditions mentioned above are satisfied. The Backup Options dialog box will allow you to select only Continuous Data Protection if this is true.
• The same file cannot be backed up more than once in the same second.
• For data with frequent changes, CDP can be configured to wait a specified amount of time from the last change made to a file before backing it up.
• File Change Detection is configurable at the backup set level.
• Windows Built-in File Monitoring (Windows only): Interfaces with Windows operating system functionality for notification of file changes.
• File Alteration Monitor (Linux only): Similar to the Windows Built-in File Monitoring. Interfaces with Linux operating system functionality for notification of file changes. FAM will only be used if it is installed and working on the target machine (i.e. if the FAM daemon can be started). If FAM is not installed, DS-Client will try to copy and execute a FAM instance on a target Linux machine.
NOTE: FAM might not be available for some UNIX platforms.
• Generic Scanner (UNIX only): Loops the scanning function from online File system backup sets. (This can be used if the File Alteration Monitor is not available. It permits CDP of any file data at the expense of a higher I/O load.)
• MLR Email Monitoring (Windows only): Monitoring included with the DS-MLR service installation.
• Windows DS-Clients can perform CDP only if the target backup machine is supported. It does not support servers that are ‘simulated’ as Windows machines (e.g. using SAMBA to back up a UNIX machine).
• CDP with BLM (Infinite Generations) will start Archiving activities as needed. While an archiving activity is in progress, the BLM will deny access to the package that is currently open for activities like Browse, Create Restorable Image, Retention, etc. DS-System will stop the current archiving activity after 5 minutes of inactivity, and re-start a new one if needed.
• The Process Window for CDP backup sets always shows the current data transfer rate. (For online backup sets, this number is the average transfer rate achieved since the start of the backup.)
CDP with other activities
Some activities are handled differently when interacting with CDP backup sets. Each CDP backup set has on/off settings to suspend the backup for scheduled Retention, Validation, and BLM (Backup Set Properties > Options : Continuous Data Protection).
• If the suspend setting is “off”, the other (scheduled) activity will fail to run with an error.
• If the suspend setting is “on”, (or if you run an on demand activity), DS-Client will suspend the CDP and resume or restart after the other (scheduled / on demand) activity finishes.
Suspend CDP, then resume:
• Restore
• BLM Request
• Validation (without errors)
Suspend CDP, then restart a new CDP:
• Synchronization
• Retention
• Delete
• Validation (with errors)
Daily Admin / Weekly Admin:
The strategy is configurable.
To configure the strategy, click Setup > Configuration > Parameters: CDP Strategy.
• Skip: Admin will skip any running CDP backup sets
• Suspend: Admin will suspend any running CDP backup sets, then restart them once the Admin is finished.
CDP should not be running:
The CDP backup set should not be in use if you run any of the following activities (you will not be allowed to proceed until the CDP backup is stopped):
• Assisted Delete (If a CDP backup is running, that backup set will be skipped)
• Remove backup set
• Disc/Tape Request
Scheduled CDP backups
A backup schedule can include the following tasks:
1. Perform Backup
2. Enforce Retention
3. Perform Validation
4. Perform BLM
For online backup sets, tasks 1-4 will run in sequence.
If the schedule applies to a CDP backup set, tasks 2-4 are handled differently. The schedule will run those tasks in the following sequence, then the CDP backup will resume / restart:
1. Perform Backup: A full scan and backup of the changed items is performed once.
2. Enforce Retention: Suspend CDP, enforce retention, then restart a new CDP
3. Perform Validation:
• If validation is completed without errors, suspend CDP, then resume.
• If validation is completed with errors, suspend CDP, then restart a new CDP.
4. Perform BLM: Suspend CDP, perform BLM, then resume.
5. After the last task is run, the CDP backup is restarted / resumed.
NOTE: The next day, when the CDP backup reaches the same scheduled start time, DS-Client will force a full scan of all files/folders in the CDP backup set’s backup items.
Bandwidth considerations (catch-up, queuing, granularity)
• If network bandwidth is slow, DS-Client queues the list of changed files. The backup is performed later, as network resources permit, using the latest change to the queued file. This means less granularity (dynamic adjustment to granularity).
• If there are too many queued changes, a pre-scan of the entire backup set will be performed.
Reconnection
Both demand and scheduled CDP backup sets will use the reconnection settings from DS-Client Setup > Configuration > Parameters and see options in the Backup Options section.
Unix DS-Client with File Alteration Monitor:
If DS-Client cannot access a backup item’s parent folder when the backup starts, DS-Client will re-check if it can be accessed every 5 minutes.
Disabling CDP in a backup set
To disable CDP in a backup set in which CDP has been enabled, do the following:
1. If a CDP backup session for the backup set is in progress, stop the backup session.
2. In the Backup Sets tree, right-click the backup set, and then click Properties.
3. In the Backup Set Properties dialog box, select the Options tab.
4. In the Options tab of the Backup Set Properties dialog box, clear the Continuous data protection box.
5. Click Apply and then click OK.