LVM snapshot function in RHEL

In RHEL, the LVM snapshot function allows you to create a snapshot volume at a certain time point for a specific LV. When a snapshot volume is created, the metadata of the source volume is copied. When a block in the source volume is modified, the block is copied to the snapshot volume before modification. For example, if a file named 1.txt occupies a block of, the block before modification will be copied to the snapshot volume. It should be noted that the unused block in the source volume is written into the content and will still be copied. For example, the block numbered 2000 is not used, that is, the value in the block bitmap is 0. At this time, a new file in the source volume occupies this block, and the block will still be copied to the snapshot volume. In this way, the snapshot volume is the exact copy of the source volume at a certain time point, even if the block is not used, it must be saved. Www.2cto.com does not feel necessary. When the snapshot is restored, copy the modified data back. blocks that are not used before and are used only in the source volume after the snapshot is created, set 0 in the block bitmap to OK. That is to say, the metadata copied from the snapshot volume is overwritten. If the snapshot volume does not copy blocks that were not used in the past, the performance should be improved, but it may not be safe enough, because after the restoration, the source volume does not return to the status when the snapshot is created, the data written afterwards still exists, but is identified as unused blocks.