what is linux snapshot

In Linux, a snapshot is a read-only point-in-time copy of the file system state. It saves the file system state at a specific time node and is saved on the same storage device as the file system; it functions as an online Data backup and recovery. Usually the system snapshot will contain all directory and file information, or at least save the file information required by the operating system.

#The operating environment of this tutorial: linux5.9.8 system, Dell G3 computer.

What is a snapshot?

A snapshot is a read-only point-in-time copy of the file system state.

Snapshot is like the literal meaning: a photo taken by taking a quick photo.

Because if you want to truly understand something deeply, you have to do some "dangerous" things. For example, if you want to see a person missing a certain part of his body or make him increase a certain part, it is impossible to do it on a real person. Do, then you need a snapshot. A snapshot is equivalent to a complete copy of the person. You can do some operations at will. Even if the photo is broken, it will be fine. Just take another photo. (Note: The real "person" in the snapshot cannot be moved when using the snapshot. It is equivalent to a mirror. If the person leaves, there will be no one in the mirror).

The role of snapshots: mainly to enable online data backup and recovery.

① When an application failure occurs on the storage device or the file is damaged, rapid data recovery can be performed to restore the data to the state at a certain available point in time.

② Provides another data access channel for storage users. When the original data is processed by online applications, users can access snapshot data and use snapshots for testing and other tasks.

All storage systems, no matter high, medium or low-end, as long as they are used in online systems, snapshots become an indispensable function.

The difference between Linux system snapshots and backups

Backup refers to copying a copy of a file and saving it to another location. Backups rarely back up the entire disk, which is usually called disk imaging or disk cloning. This type of backup actually mirrors the entire disk, including user data, operating system, boot partition, etc. Disk images can be used in bare metal recovery efforts. At this time, you can copy the entire contents of a hard drive to another computer without installing an operating system.

And System snapshot (Snapshot) saves the state of the file system at a specific time node and saves it on the same storage device as the file system. Usually the system snapshot will contain all directory and file information, or at least save the file information required by the operating system.

Saving the snapshot and file system in the same location enables the possibility of rollback and also helps save disk space. In this case, each time a new system snapshot is created, it is not necessary to save the entire state of the entire file system. To put it figuratively, a system snapshot is like an ever-growing backup process. Each time it only saves information changes that are different from the last time. This means that each system snapshot must depend on the last system snapshot so that it can be completely completed. The system resumes work. On the contrary, a complete disk backup or disk image is independent of other backup files and can complete system recovery work independently.

The problem you may encounter with system snapshots is that they are very vulnerable to hard drive failure. If your hard drive has suffered severe physical damage, it's likely that your system snapshot won't be able to help you restore your system. To prevent this, we recommend taking a system snapshot immediately after installing and setting up your Linux system, and then copying it separately to another storage device.

There are some applications in Linux that can help you save system snapshots. Most applications are aimed at novice users and do not require advanced Linux operating skills. We’ve picked out a few here so you can choose the app that’s right for you.

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