I have a Windows 2008 R2 server named Server that runs a backup each night to an encrypted USB drive attached to the server. I shared the drive on the server as shown below and configured Windows Server Backup to backup to the local shared folder.
- \\Server\Backup
Everything worked well for several months with the backup speeds being about 1 GB/min (15 to 20 MB/s). At the beginning of this week, I noticed that the backup speeds reduced to 1 to 2 MB/s which resulted in the backup not completing before the encrypted disk was automatically dismounted.
After much research and testing, I believe that I have narrowed down the cause of the issue to an issue writing data to the local UNC path of \\Server\Backup as shown by comparing the following tests.
Test 1
- c:> copy largefile h:\
The above DOS command copies the file to the encrypted drive mounted at h:\ quickly.
Test 2
- c:> copy largefile \\Server\Backup
The above DOS command copies the data to the same location but was 33x slower that the Test 1 DOS command.
I duplicated the above results using the xcopy command instead of the copy command but could not duplicate the above results on my Windows 7 computer. On my Windows 7 computer, the two versions of the copy performed the same.
The following are some additional observations:
- If I change the backup location to an external UNC like \\Sever2\Backup, everything works well.
- After repeatedly running Windows Server Backup after make changes such as restarting the server and tweaking the NIC parameters, the backup will all of a sudden start backing up at the normal speed but this will only last for about an hour before it reduces back to the slow backup speed.