Backup
[note 1][4] There are also different ways these devices can be arranged to provide geographic dispersion,[5] data security, and portability.
2 or more different media should be used to eliminate data loss due to similar reasons (for example, optical discs may tolerate being underwater while LTO tapes may not, and SSDs cannot fail due to head crashes or damaged spindle motors since they do not have any moving parts, unlike hard drives).
An offsite copy protects against fire, theft of physical media (such as tapes or discs) and natural disasters like floods and earthquakes.
Because there is no perfect storage, many backup experts recommend maintaining a second copy on a local physical device, even if the data is also backed up offsite.
[8][9][10][11] An unstructured repository may simply be a stack of tapes, DVD-Rs or external HDDs with minimal information about what was backed up and when.
A repository using this backup method contains complete source data copies taken at one or more specific points in time.
Typically a full backup of all files is made once or at infrequent intervals, serving as the reference point for an incremental repository.
[15] Near-CDP backup applications use journaling and are typically based on periodic "snapshots",[16] read-only copies of the data frozen at a particular point in time.
This backup method differs from simple disk mirroring in that it enables a roll-back of the log and thus a restoration of old images of data.
Intent-logging allows precautions for the consistency of live data, protecting self-consistent files but requiring applications "be quiesced and made ready for backup."
Software may create copies of individual files such as written documents, multimedia projects, or user preferences, to prevent failed write events caused by power outages, operating system crashes, or exhausted disk space, from causing data loss.
Magnetic tape was for a long time the most commonly used medium for bulk data storage, backup, archiving, and interchange.
[22] Tape is a sequential access medium, so the rate of continuously writing or reading data can be very fast.
[23] However, hard disk backups are close-tolerance mechanical devices and may be more easily damaged than tapes, especially while being transported.
[24][31][25] External hard disks can be connected via local interfaces like SCSI, USB, FireWire, or eSATA, or via longer-distance technologies like Ethernet, iSCSI, or Fibre Channel.
Recordable CDs, DVDs, and Blu-ray Discs are commonly used with personal computers and are generally cheap.
[37] Many optical disc formats are WORM type, which makes them useful for archival purposes since the data cannot be changed in any way, including by user error and by malware such as ransomware.
Moreover, optical discs are not vulnerable to head crashes, magnetism, imminent water ingress or power surges; and, a fault of the drive typically just halts the spinning.
Flash memory, thumb drives, USB flash drives, CompactFlash, SmartMedia, Memory Sticks, and Secure Digital card devices are relatively expensive for their low capacity, but convenient for backing up relatively low data volumes.
[43] Cloud-based backup (through services like or similar to Google Drive, and Microsoft OneDrive) provides a layer of data protection.
[25] However, the users must trust the provider to maintain the privacy and integrity of their data, with confidentiality enhanced by the use of encryption.
These media management methods are not mutually exclusive and are frequently combined to meet the user's needs.
This type of storage is convenient and speedy, but is vulnerable to being deleted or overwritten, either by accident, by malevolent action, or in the wake of a data-deleting virus payload.
A mechanical device is usually used to move media units from storage into a drive where the data can be read or written.
Because the data is not accessible via any computer except during limited periods in which they are written or read back, they are largely immune to on-line backup failure modes.
The vault can be as simple as a system administrator's home office or as sophisticated as a disaster-hardened, temperature-controlled, high-security bunker with facilities for backup media storage.
Due to high costs, backing up is rarely considered the preferred method of moving data to a DR site.
This is also the case across interrelated files, as may be found in a conventional database or in applications such as Microsoft Exchange Server.
Accurately recovering a complete system from scratch requires keeping track of this non-file data too.
High-capacity removable storage media such as backup tapes present a data security risk if they are lost or stolen.
