Is it is possible to replace one array to other new 8 HDD array in HP RAID 1+0 without losing data on old array?

Solution 1:

HP Smart Array solutions keep the RAID configuration on disk. If you remove the old disk set and keep the drives in order (labeled 1 through 4), you can use them with any similar-generation controller. They would still constitute a bootable array/logical drive.

When you talk about keeping the old disks as a backup, are you just thinking about using it as a fall-back solution? But you still have a backup process in place... What would happen to the 4 disks after you migrate?

Why are you moving to 8 disks? Space? Speed?

You could safely replace the 4 disks with 4 of the larger disks (assuming that they're larger) and add the additional 4 disks. From there, you could perform an online RAID resize/transformation that will redistribute data across the new drives.

This can be done entirely online without any downtime.

Please take a look at the HP Smart Array Reference Manual and its section on Array Expansion and Migration.