[eng] Целостность и проверка данных. Резервное копирование данных.
Advantages We can recover data if the original data will be lost You can store multiple copies in different locations Disadvantages You will need extra memory to store a copy If your backup will be in the same room as the original, then in case of fires, floods, this will not save your data When mirroring, all involved disks are exact copies of each other. The default data synchronization is performed. Advantages This technology is simple and easy to implement. Provides high fault tolerance when working with two disks. If one hard drive fails, the data can be retrieved from the other mirrored hard drives. Disadvantages The usable storage capacity is only half of the total disk capacity. You cannot replace a failed drive while the computer is running. If a virus attaches to a file and starts replicating, this will also happen on the mirrored disk. If you accidentally delete a file on one disk, it will be deleted on the other.
A backup is the creation of a copy of data or files for storage on another disk or on another server.
Disk mirroring is the replication of data across two or more disks.
Validation is a check to make sure that the entered data meets the requirements.
Type of validation |
How it works |
Example usage |
Check digit |
one or several digits in a code are used to check the other digits are correct |
algorithm Luna check last digit in credit card, bar code readers in supermarkets use check digits |
Format check |
checks the data is in the right format |
a motorbike number in Kazakhstan is in the form NN NN LL where L is any letter and N is any number |
Length check |
checks the data isn't too short or too long |
a password which needs to be eight letters long |
Presence check |
checks that data has been entered into a field |
in most databases a key field cannot be left blank |
Range check |
checks that a value falls within the specified range |
number of hours worked must be less than 50 and more than 0 |
Character check |
When a field has to contain a specific character or type of characters. |
an e-mail address should contain an “@” sign |
Type check |
when a field has be of a certain data type |
integer, float/real |
