Mixing brand model and size to upgrade storage space?

mdgm wrote:
That's not the only option. Take a look at http://www.readynas.com/RAIDiator_x86_4_2_12_Notes Check your partition.log. If you have the time or if most of your disks are not 4k sector aligned then it would be best to backup and do a factory reset but that is not the only option.

mdgm,
I've checked partition log. Seems all 4 disks are 512 sector.
So i'm afraid i will need to full backup and factory reset my NAS prior to expand my array.

I have an other "small" NAS and several external USB HDD, but i miss a single backup volume with sufficent space (2TB) .
Any pointer to a full data backup procedure (near 2TB needed) on several devices ?
Thank you

partition.log extract

***** partition output for sdd *****

Disk /dev/sdd: 1953525168 sectors, 931.5 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 9BF39102-7D95-4343-ABFF-489B348716D5
Partition table holds up to 8 entries
First usable sector is 4, last usable sector is 1953525164
Partitions will be aligned on 8-sector boundaries
Total free space is 5101 sectors (2.5 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1               4         8388611   4.0 GiB     FD00  Linux RAID
   2         8388612         9437187   512.0 MiB   FD00  Linux RAID
   5         9437189      1953520064   927.0 GiB   FD00  Linux RAID

Disk /dev/sdd: 121601 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8257536 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start     End   #cyls    #blocks   Id  System
/dev/sdd1          0+ 121126- 121127- 976762583+  ee  EFI GPT
/dev/sdd2          0       -       0          0    0  Empty
/dev/sdd3          0       -       0          0    0  Empty
/dev/sdd4          0       -       0          0    0  Empty