Thanks George, I have changed the Log Backup Frequency to one hour.

I ran again DBCC SQLPERF(LogSpace) and it shows around 14 GB but I was looking Backup Log on my backup drive it also shows.

see the result:

Log Size (MB) Log Space Used (%) Status

14198.8 2.486978 0

I have just checked - select name,log_reuse_wait_desc from sys.databases and log_reuse_wait_desc shows Log_backup and also checking to VLfs, total files around 490 and 33 files with status = 2.

I have changed T-log backup frequency to every one hour, now backup log size is every hour is:

8 AM 7013 KB

9 AM 24897 KB

10 AM 45385 KB

11 AM 43220 KB

12 PM 419318 KB

Thanks