br: update documents for br scenario (pingcap#6673)

br/backup-and-restore-tool.md

@@ -8,7 +8,9 @@ aliases: ['/docs/dev/br/backup-and-restore-tool/','/docs/dev/reference/tools/br/
 
 [BR](http://github.com/pingcap/br) (Backup & Restore) is a command-line tool for distributed backup and restoration of the TiDB cluster data.
 
-Compared with [`dumpling`](/backup-and-restore-using-dumpling-lightning.md), BR is more suitable for scenarios of huge data volume.
+Compared with [`dumpling`](/backup-and-restore-using-dumpling-lightning.md), BR is more suitable for scenarios involved huge data volumes.
+
+In addition to regular backup and restoration, you can also use BR for large-scale data migration as long as compatibility is ensured.
 
 This document describes BR's implementation principles, recommended deployment configuration, usage restrictions and several methods to use BR.
 
@@ -187,6 +189,7 @@ The following are some recommended operations for using BR for backup and restor
 - It is recommended that you execute multiple restore operations serially. Running different restore operations in parallel increases Region conflicts and also reduces restore performance.
 - It is recommended that you mount a shared storage (for example, NFS) on the backup path specified by `-s`, to make it easier to collect and manage backup files.
 - It is recommended that you use a storage hardware with high throughput, because the throughput of a storage hardware limits the backup and restoration speed.
+- It is recommended that you disable the checksum feature (`--checksum = false`) during backup operation and only enable it during the restore operation to reduce migration time. This is because BR by default respectively performs checksum calculation after backup and restore operations to compare the stored data with the corresponding cluster data to ensure accuracy.
 
 ### How to use BR