A comparison of block-level and file-level backups
Data backup is to restore the data and system information required by the computer system as soon as possible. It not only plays a protective role in the case of hardware failure or human error of the network system but also can take over the basis of critical business in the case of failover backup machine in the cluster environment. Of course, data backup is also one of the prerequisites for system disaster recovery.
From the backup mode point of view, there are physical and logical backups, which are commonly referred to as file-based backups and block-based backups. For Vinchin Backup & Recovery, backup based on the data block level. Also, Vinchin can do the backup of file level.
What are physical and logical backups?
Physical backup: A physical backup is a copy of data from the host to a backup machine in the basic unit of a disk block.
Logical backup: A logical backup is a file-based copy of data from the host to a backup.
Then we will discuss in detail the differences between the two backup modes respectively in terms of the efficiency, real-time, and support of backup:
1. High efficiency
The physical backup is under the file system and above the hardware disk drive. A soft driver has been added, which ignores files and structures, has a clean processing process, and therefore has less overhead in search operations during execution and high backup performance.
Logical backups are file-based backups because each file is made up of different logical blocks. Each logical file block is stored on a contiguous physical disk block, but the different logical blocks that make up a file are most likely to be stored on separate disk blocks. Logical Backup Requires additional lookup operations when backing up files on discontinuous storage disks. These additional operations increase disk overhead and reduce disk throughput. As a result, backup performance is poor compared to physical backups.
Physical backup avoids the need to back up the entire file when there is a small change in the file, but only the backup of the changes, which effectively improves the backup efficiency and saves the backup time.
In logical backup mode, the entire file needs to be backed up even with a small change. In this way, if a file is large, it will greatly reduce the backup efficiency, increase disk overhead, and backup time.
2. The real-time
Physical backup can achieve efficient real-time backup, because every time the host writes to the disk, the data needs to be written to the backup machine at the same time, this kind of write operation is based on the disk sector, so, it can be recognized very quickly. Only after the backup is complete will it be returned to the upper application system for further work.
Logical backup is difficult to achieve real-time backup because every modification is based on the file, and which part of the file is modified, the system is difficult to capture in real-time, so the backup needs to read the whole file and then send it to the standby machine, real-time efficiency is not very high.
Physical backup copies data under the file system, so it is not restricted by the file system and can support a variety of file systems including RAW partitions.
Logical backup copies data as a single file, so it is limited by the file system and can only backup partially supported file systems. RAW partitions are not supported.
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