Windows 7 - External hard drive image failed

Hi, I have two internal 500Gb SATA drives and one external 500Gb ESATA drive.
I wanted to have 2 backups images of my drive as a safety measure. One on the internal and one on the external ESATA drive.
The backup image on the internal drive took about 25 minutues and seems OK. The image size is about 75Gb.
I then tried a second backup on my external drive. ESATA is supposed to be faster than USB. After about three and a half hours the backup stopped and said that it had failed. Any ideas please?
Thanks in advance!
Graham

What did the error say? and i assume you create your image using the "Backup and Restore"

Yes I did use the "backup and restore".
I can't remember the exact wording of the error message, but it seemed to loose connection with my ESATA drive. I wasn't using the computer at the time.
I think I will give it another go later. The problem is if some how it did lose the connection, I wont ever trust it to do a restore.
Graham

I didn't have any issue with normal USB to Firewire seagate external. But my size cam to 55Gb. Maybe give your eSATA another go, and then use normal USB to see it that works.