Yeah, looks like the command just hangs indefinitely on /dev/sdb.
stat("/dev/loop6", {st_mode=S_IFBLK|0660, st_rdev=makedev(0x7, 0x6), ...}) = 0
openat(AT_FDCWD, "/dev/loop6", O_RDONLY|O_DIRECT|O_NOATIME) = 3
fstat(3, {st_mode=S_IFBLK|0660, st_rdev=makedev(0x7, 0x6), ...}) = 0
ioctl(3...