Gentlemen, thanks for your help. To answer:
yancek: this is MBR, Grub2 on sda8 (debian jessie), modified by update-grub. When the grub screen appears, it shows the partitions on sdb (usb disk) as well as those on sda, but it does not boot the one copied by dd.
jefro: I didn't make a note of the dd command used. It was just a simple if to of with 4096 blocks.
My grub has no "find" command, but the grub "ls" command shows
Code:
grub> ls
(hd0) (hd0,msdos9) (hd0,msdos8) (hd0,msdos7) (hd0,msdos6) (hd0,msdos5) (hd0,msdos1) (hd1) (hd1,msdos4) (hd1,msdos2) (hd1,msdos1)
It does not show (hd1,6) which is the OS partition copied by dd.
I do not intend to boot from the dd partition, but to have my normal grub boot it.
Emerson: the MBR on sda boots (thru grub on sda8) all OS partitions on sda as well as the one installed (not copied) on sdb1.
Matt Green: I modified the fstab on the dd partition, replacing the UUID that dd copied from sda1 with the UUID assigned to the dd partition.