What is physical Backup?
The operating system saves the database files onto tape or some other media. This is useful to restire the system to an earlier point whenever needed. In its simplest form, a physical backup is the movement of all data from one raw device to another; in the context of file system backup the source devices are disks and the destination, devices may include disk, CD-Rom, floppy, Zip drives, and of course, tape.All file systems must have some way of determining which blocks are free, and the backup procedure can interpret that information to only back up the blocks that are in use. Naturally, this requires that the block address of each block written to the backup medium be recorded so that restore can put the data back where it belongs.
Advantages of Physical Backup are given below:-
- The primary benefits of a physical backup scheme are simplicity and speed. It is simple because every bit from the source device is copied to the destination; the format of the data is irrelevant to the backup procedure. It is fast because it is able to order the accesses to the media in whatever way is most efficient. There are a number of limitations to physical backup, however.
- The Physical backup data is not interpreted when it is written, it is extremely non-portable; the backup data can only be used to recreate a file system if the layout of the file system on disk has not changed since the backup was taken. Depending on the file system organization, it may even be necessary to restore the file system to disks that are the same size and configuration as the originals.
- Restoring a subset of the file system (for example, a single file which was accidentally deleted) is not very practical. The entire file system must be recreated before the individual disk blocks that make up the file being requested can be identified.
- The file system must not be changing when the backup is performed, otherwise, the collection of disk blocks that are written to disk will likely not be internally consistent. Finally, the coarse-grained nature of this method leads to its own difficulties. Because file system information is not interpreted by the backup procedure, neither incremental backups nor backing up less than entire devices is possible. A raw device backup is analogous to a fire hose. Data flows from the device simply and rapidly — but it is all you can do to hold the hose. Finer grained control is generally impossible.
- Easy Storage – Most tape formats offer a large storage capacity in a relatively small physical package. Cartridges like LTO-6 give businesses an easy way to back up enterprise-level systems without dedicating entire rooms to server hardware
- Dependability – Tape cartridges are not particularly susceptible to physical or electronic damage. They can safely store data for years or decades without suffering from problematic media decay or corruption. However, you need to protect tapes from excessive humidity and extreme temperatures.
- Low Overall Costs – Tapes cost less in terms of electricity and administration. Media is also fairly affordable in the long-term.
- Simple Replication – Large businesses can easily make physical copies of mission-critical tape backups. Many formats offer advanced encryption features for enhanced security, which improves the utility of each individual backup.
Disadvantages of Physical Backup are mention below:-
- Potential Media Issues – While data tapes resist physical damage, they gradually wear down over time. Most tape cartridges have a rated storage life of 20-30 years in perfect conditions, but factors like humidity and temperature can cause potentially serious media issues.
- Limit Scalability – While tapes take up the less physical room than hard drives, scalability is limited by the capacity of the format. Businesses that use tape drives will eventually need to update to new formats.
- High Setup Costs – Installing a new tape system takes a tremendous investment. Businesses need to regularly purchase media and pay ongoing costs for system management.
- Slow Access Speeds – Some tape formats use specialized file systems that allow for relatively fast access to individual files. However, no data tape format allows for true random access to data.
Modes to take physical backup:-
User-Managed Backup: -Backup means taking copy of our database which is overcome for database failures and with that backup we can recover database whenever it crash.User-managed backup and recovery is any strategy in which Recovery Manager (RMAN) is not used as the principal backup and recovery tool. The basic user-managed backup strategy is to make periodic backups of datafiles and archived logs with operating system commands.
RMAN Backup: – Recovery Manager is a tool that manages the process of creating backups and also manages the process of restoring and recovering from them.RMAN uses the configured settings and channels for your database, the record of previous backups in the RMAN repository and the control file’s record of the structure of your database to determine an efficient set of specific steps to perform in response to a BACKUP command and then carries out those steps.