RAIDs

RAID1 is data mirroring. Two copies of the data are held on two physical disks, and the data is always identical. RAID1 has a performance advantage, as reads can come from either disk, and is simple to implement. However, it is expensive, as twice as many disks are needed to store the data.
RAID3 A block of data is striped over an array of disks, then parity data is written to a dedicated parity disk. Successful implementations usually require that all the disks have synchronised rotation. RAID3 is very effective for large sequential data, such as satellite imagery and video.
RAID4 data is written in blocks onto the data disks (i.e. not striped), then parity is generated and written to a dedicated parity disk.

Backup

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Antivirus

Antivirus software can prevent malicious software from running on your computer. Malicious
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Physical security

Physical security as a method of preventing data loss can be highly effective when used correctly. By locking doors, using Kensington Locks or having somebody guarding the area where the data is stored can prevent somebody from physically stealing any data or having access to it where they could delete the data.