I have an Areca ARC-1880IX-24 RAID Controller (FW 1.51) with several different Seagate 3TB disks (SAS and SATA, and of different age) attached to it to form a RAID5. When I tried to expand it by two disks too many failed during data migration and the data was lost. This was "just" the backup, so the data is still save on the other main RAID of level 6.

I had one more spare disk and a colleague lent me another one (which I have to give back) so I have enough to set up a new RAID5 with the original disk space. Of course I want my backup up and running again as soon as possible and I also decided to upgrade the backup RAID to level 6. Unfortunately, it will take up to 2 weeks for new disks to be delivered.

I now have the following possibilities:

  1. Create the original setup and copy the data. After two weeks: Switch the lent disk for a new one and then add enough disks to expand disk space and upgrade RAID level.
  2. Create a RAID6 with less space now and copy the data. In two weeks switch the lent disk and then expand the RAID to the disk space I was aiming for in the first place.
  3. My colleague can lent me 2 more disks, so I could set up a RAID6 with the final disk space now, copy the data and in two weeks simply switch the lent disks.
  4. Some idea you might have that I didn't think of.

My question now is: Is it possible to know / Can you tell me which of those scenarios would put the least stress on my disks? I would like to minimize the risk of more / too many disks failing in two weeks, because then I might have to pipe my 30TB through the local network again.

If it's not possible to answer my question I'm prefering option 3 right now.

Thank you for your time and help,


  • As you are considering RAID5 (parity), read up on UREs
    – Lenniey
    Jan 16, 2019 at 9:18

2 Answers 2


For a parity RAID, expansion and rebuild command very similar, if not identical, disk load (an exception exists: if your RAID card and HDDs supports Fast Rebuild / Rebuild Assist and other preconditions are met, a rebuild will be much lighter than a capacity expansion).

The simpler choice would be option n.3 - to get another disk and create a RAID6 array with the right size from the start. In this manner, you should not care about capacity expansion and/or raid reshaping, but only about rebuilding the array after disk change.

  • Thanks, I went with the third one. Now I only have to wait for the new disks to be delivered.
    – noes
    Jan 22, 2019 at 14:43

Mixing SAS and SATA is not the best idea, because even if you have a single SATA in the RAID array, entire performance will be limited by this SATA disk. As per thread itself. Well, I would suggest using the second option which is less stress for the entire Array and disks itself.

  • There were already different disks in the RAID when I took it into my care. In this case the network bandwith is more the limiting case, but I will consider your remark if I ever build a new RAID, thanks.
    – noes
    Jan 22, 2019 at 14:45

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