Percona MySQL 8.0.33-25 Community Edition is running on Ubuntu 22.04 server having 64 CPU and 128 GB RAM. The volume of data is 25 TB. We are running util.dumpinstance with 55 threads but the dump is running very slow and running for 2 days, still running.
What is the root cause of this slowness and what is the solution
util.dumpinstance from mysqlshell is a full-table scan style backup. It will indeed take an extremely long time to dump 25TB. Observe CPU/Disk during the backups as this will be were the slowness comes from.
With 25TB, you should be doing either physical backups (using percona xtrabackup), or snapshots of the disk.