copy failure

[Dan Lester]

I'm doing a backup to a new Crucial 500GB SATA SSD. The progress of the copy-after-erase backup is confusing. With a 160GB total, "Replicating System Volume" starts out increasing fast, but then slows dramatically. It's half done in three minutes, and then the last 10GB takes more than thirty minutes.

Most of my other backups take place automatically, at night, so I don't watch their progress. Is this strange progress rate normal?

But then it starts "Replicating Data Volume" and SuperDuper soon gives up, with a "Failed to copy".

Log says "Completed System Volume Replication", but then while it is "Replicating Data Volume" I get

Volume replication failed - error 49158
Error | ***ERROR OCCURRED: ****FAILED****: result=256 errno=60 (No such process)

This failure happens repeatedly. What's going on?

In DiskUtility, this disk looks to be set up the same as the others.