Is SQL Server Backup single or multi-threaded?
Does SQL Server uses a separate writer thread for each backup device (backup file) or separate thread is used only when you stripe your backup across multiple backup volume (drive letter, LUN or mount point)?
for e.g. do we get three write thread here or
backup database dbName to DISK = 'D:\file1.bak', DISK = 'D:\file2.bak', DISK = 'D:\file3.bak'
OR the following speeds up the backup because you are writing to different volume
backup database dbName to DISK = 'D:\file1.bak', DISK = 'E:\file2.bak', DISK = 'F:\file3.bak'
In above each drive letter is a separate IO path. I understand IO throughput is also very important for backup speed.