Derrick Rountree, in
Security for Microsoft Windows System Administrators, 2011 Differential backups are usually used in
combination with full backups. Differential backups will only back up all files that have the archive bit set. Because of this they will take a shorter amount of time to perform than full backups or copy backups. Differential backups do not reset the archive bit. So basically, every time you perform a differential backup you will be backing up every file that changed since the last full backup was performed. Complete restores using differential backups will generally take longer to perform than
full backup restores because you will have to restore both the last full backup and the last differential backup. Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9781597495943000053 MCSE 70-293: Planning, Implementing, and Maintaining a High-Availability StrategyMartin Grasdal, ... Dr.Thomas W. ShinderTechnical Editor, in MCSE (Exam 70-293) Study Guide, 2003 Differential BackupsThe differential backup type is sometimes used as a substitute for the incremental type. A differential backup collects data that has changed or been created since the last full (normal) or incremental backup, but it does not clear the archive bit on the file. It can also be used after a copy or differential backup, but as with an incremental backup, every file with the archive attribute set is backed up. The differential backup is advantageous when you want to minimize the restoration time. A complete system restore with a full/differential backup combination, as illustrated in Figure 8.36, requires only the most recent full backup and the most recent differential backup. Differential backups start with small volumes of data after a recent full or incremental backup, but often grow in size each time, because the volume of changed data grows. This means that the time to perform a differential backup starts small but increases over time as well. In theory, if full or incremental backups are infrequent, a differential backup could end up taking as long and reaching the same volume as a full backup. Figure 8.36. Full (Normal) Backup/Differential Backup Pattern
|
Daily full | Weekly full and daily differential | Weekly full and daily incremental | |
---|---|---|---|
Recovery steps | Last backup set | Last full and last differential backup set. | Last full and all incremental backup sets since the full backup. |
Recovery issues | None | Many log files have to be replayed. | Many individual backup sets have to be restored, and many log files have to be replayed. If one incremental backup set is damaged, you can only restore to the last contiguous log file/backup set. |
Recovery time | Low | Medium to high | High |
Backup time | High | Medium | Low |
Media costs | High | Medium | Low |
Using daily full backups is a best practice. Even if you have a shorter backup window with the other backup types in Table 8-2, the recovery procedure is more complex and time consuming. Remember that you do not back up for the sake of backups. You only perform backups to be prepared for a fast recovery.
If you made the decision to have large databases because business needs justified the support for mailboxes with gigabyte quotas, you will face the issue that you cannot back up all databases using a daily full backup. Very likely your backup infrastructure is not capable of transferring terabytes of data from the mailbox server to a backup media within the backup window. In this case, you can consider using weekly full and daily differential backups. Table 8-3 shows the corresponding backup schedule.
Table 8-3. Weekly full and daily differential
Storage group | Mon | Tue | Wed | Thu | Fri | Sat | Sun |
---|---|---|---|---|---|---|---|
1 | Full | Dif | Dif | Dif | Dif | Dif | Dif |
2 | Dif | Full | Dif | Dif | Dif | Dif | Dif |
3 | Dif | Dif | Full | Dif | Dif | Dif | Dif |
4 | Dif | Dif | Dif | Full | Dif | Dif | Dif |
5 | Dif | Dif | Dif | Dif | Full | Dif | Dif |
6 | Dif | Dif | Dif | Dif | Dif | Full | Dif |
7 | Dif | Dif | Dif | Dif | Dif | Dif | Full |
… | … | … | … | … | … | … | … |
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Domain 6
Eric Conrad, ... Joshua Feldman, in CISSP Study Guide, 2010
Electronic Backups
Electronic backups are archives that are stored electronically and can be retrieved in case of a disruptive event or disaster. Choosing the correct data backup strategy is dependent upon how users store data, the availability of resources and connectivity, and what the ultimate recovery goal is for the organization.
Full Backups
A full system backup means that every piece of data is copied and stored on the backup repository. Conducting a full backup is time consuming, bandwidth intensive, and resource intensive. However, full backups will ensure that any necessary data is assured.
Incremental Backups
Incremental backups archive data that have changed since the last full or incremental backup. For example, an example site performs a full backup every Sunday, and daily incremental backups from Monday through Saturday. If data are lost after the Wednesday incremental backup, four tapes are required for restoration: the Sunday full backup, as well as the Monday, Tuesday, and Wednesday incremental backups.
Differential Backups
Differential backups operate in a similar manner as the incremental backups except for one key difference. Differential backups archive data that have changed since the last full backup.
For example, the same site in our previous example switches to differential backups. They later lose data after the Wednesday differential backup. Now only two tapes are required for restoration: the Sunday full backup and the Wednesday differential backup.
Electronic vaulting
Electronic vaulting is the batch process of electronically transmitting data that is to be backed up on a routine, regularly scheduled time interval. It is used to transfer bulk information to an offsite facility. There are a number of commercially available tools and services that can perform electronic vaulting for an organization. Electronic Vaulting is a good tool for data that need to be backed up on a daily or possibly even hourly rate. It solves two problems at the same time. It stores sensitive data offsite and it can perform the backup at very short intervals to ensure that the most recent data is backed up.
Because electronic vaulting occurs across the Internet in most cases, it is important that the information sent for backup be sent via a secure communication channel and protected through a strong encryption protocol.
Remote Journaling
A database journal contains a log of all database transactions. Journals may be used to recover from a database failure. Assume a database checkpoint (snapshot) is saved every hour. If the database loses integrity 20 minutes after a checkpoint, it may be recovered by reverting to the checkpoint, and then applying all subsequent transactions described by the database journal.
Remote Journaling saves the database checkpoints and database journal to a remote site. In the event of failure at the primary site, the database may be recovered.
Database shadowing
Database shadowing uses two or more identical databases that are updated simultaneously. The shadow database(s) can exist locally, but it is best practice to host one shadow database offsite. The goal of database shadowing is to greatly reduce the recovery time for a database implementation. Database shadowing allows faster recovery when compared with remote journaling.
HA options
Increasingly, systems are being required to have effectively zero downtime, an MTD of zero. Recovery of data on tape is certainly ill equipped to meet these availability demands. What is required is the immediate availability of alternate systems should failures or disaster occur. A common way to achieve this level of uptime requirement is to employ a high availability cluster.
Note
Different vendors use different terms for the same principles of having a redundant system actively processing or available for processing in the event of a failure. Though the particular implementations might vary slightly, the overarching goal of continuous availability typically is met with similar though not identical methods, if not terms.
The goal of a high availability cluster is to decrease the recovery time of a system or network device so that the availability of the service is less impacted than would be by having to rebuild, reconfigure, or otherwise stand up a replacement system. Two typical deployment approaches exist:
•Active-active cluster involves multiple systems all of which are online and actively processing traffic or data. This configuration is also commonly referred to as load balancing, and is especially common with public facing systems such as Web server farms.
•Active-passive cluster involves devices or systems that are already in place, configured, powered on, and ready to begin processing network traffic should a failure occur on the primary system. Active-passive clusters are often designed such that any configuration changes made on the primary system or device are replicated to the standby system. Also, to expedite the recovery of the service, many failover cluster devices will automatically, with no required user interaction, have services begin being processed on the secondary system should a disruption impact the primary device. It can also be referred to as a hot spare, standby, failover cluster configuration.
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