SQL databases are widely used in small and medium-sized enterprises as warehouses for data storage. However, due to some failure reasons, the SQL database will be damaged and data will be lost. This article mainly talks about several common failures of several SQL databases and recovery techniques for fragmented SQL databases.
SQL database "823" error
Fault manifestation: Due to the loss of buffer data, the database cannot write correct data, resulting in disordered data structure. After restarting, the database cannot be attached normally. When attaching the database file MDF and log file LDF, an "823" error is reported.
Analysis of the cause of the failure: This situation is mostly caused by a sudden crash or power failure during the database read and write process, or the database appears in a "doubtful" state after the server is restarted, or it may be caused by a disk I/O error. Due to the loss of buffer data, the database cannot write correct data, resulting in disordered data structure, and the database cannot be attached normally after restarting.
SQL Database "Internal Consistency Error"
Failure performance: "Internal Consistency Error" occurs when restoring a database from a previously backed up database. It is obvious that a backup was made, but the backup file was found to be damaged when restoring. This means the loss of the database, the consequences are very serious.
Failure cause analysis:
1) The backup file and the database are placed on the same physical hard disk. If the hard disk fails, the backup is also damaged.
2) The backup medium is damaged; or it is a network backup, and the data is damaged during network transmission.
3) When the database is doing a full backup, file backup or file group backup, the contents in it are already damaged.
4) This error also occurs when the backup MDF file is incomplete due to bad sectors in the disk when backing up the database.
Accidentally deleted or formatted SQL database
Failure performance: SQL data files are deleted by mistake, formatted, partitioned by mistake, Ghost by mistake, and reinstalled the system, resulting in loss of SQL Server database files.
Failure cause analysis: When the FAT32 deletes or formats the file or deletes the file in the NTFS partition, the file length becomes 0 bytes. MDF database file disks are often stored in discrete logical clusters, forming file fragments. When deleted or formatted, these fragmented data scattered on the disk are difficult to recover.
As long as there are data files, the data recovery center can restore the SQL database to the greatest extent, and engineers can perform massive calculation, reorganization and recovery of each fragmented data, and restore the data completely.