Today I was working on an issue in which backup job was showing in executing state since last 2 days.Initially my observation was either it was hung in middle of its process or it was processing very slow.Here i decided to see the lock wait type for this process.when i gather this info i see the wait type was BACKUPBUFFER wait type.
BACKUPBUFFER Wait Type:-This wait type Occurs when a backup task is waiting for data, or is waiting for a buffer in which to store data. This type is not typical, except when a task is waiting for a tape mount. This wait stats will occur when you are taking the backup on the tape or any other extremely slow backup system.This wait type can be seen with one more wait type i.e. ASYNC_IO_COMPLETION.
These both wait type indicates that the issue is with storage/disk subsystem.So solution is to either ask your storage team to look in this or change your disk/storage subsystem and run your backup on a healthy and fast storage subsystem.