I recently moved my laptop backups to an Acomdata external hard drive. I noticed that it mounted two partitions, a hard drive partition and a CD partition, but did not worry too much about it since I had plenty of disk space on the hard drive partition. The CD partition was created by the manufacturer to store their disk utilities and, like a normal CD, appeared to my laptop as read-only. After saving multiple backups to this disk, I received a new internal hard drive and tried to restore from the backups on the external hard drive. However, I could not boot to the external hard drive because my laptop would only recognize the CD partition during boot, not the hard drive partition. [more]
After some Googling, I discovered that these CD partitions have caused quite a few issues, including not allowing some Linux distributions to mount the hard drive partition. The easiest fix at first seemed to be to take the hard drive out of the external casing, connect directly to a desktop PC's internal hard drive controller and re-partition/format the entire drive. Right before giving in to this solution, I found a blog post on LinkedIn which is no longer available.
This author spent some time with Acomdata support and got them to provide a software tool to remove the CD partition while it is connected externally via USB. In the end, I moved my data off of the external hard drive, ran the tool, formatted the external hard drive as a single partition, moved my data back, and was able to boot/restore from the external hard drive. I even have a little bit of extra space now that the CD partition is gone.