Increasing drive capacity on PR4100

Hello folks,

Been happily running with the 4 bay PR4100 for a couple of years now with x4 3TB drives, Raid 5. I’m now down to just under 3TB of storage left, so I’m now thinking about increasing my capacity by adding two new Red drives, thinking about x2 6TB, to give new total of 18TB.

Am I right in thinking that this is a straight forward process of just pulling two of the exisiting 3TB drives and replacing them with the two new 6TB drives, and that Raid 5 will just automatically re-build on the two new drives over a couple of days? Never done this before, so nervous as hell just thinking about it!

Thanks in advance for any advice offered.

Best wishes,


RAID 5 configuration requires minimum 3 drives of same capacity and It is recommended to utilise the remaining storage left in the My Cloud PR device and remove the filled drive from the enclosure and upgrade the capacity of the device.

In RAID 5, if you change all the drives with upgraded capacity of 6TB each, you will get 18TB (75% of total capacity) as usable capacity.

I’m not sure I understand the answer here.

You’re saying take one drive out and upgrade at a time?

Take one out>Put New in> Let Rebuild>Repeat?

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This is not a pr4100

Hi Davys,

I am probably necroind the dead thread, but just for probability that you did not found your answer yet…
I expanded capacity of my PR4100 in past month. Unfortunately, what you want to do is not possible as per my knowledge. You need 4 same capacity drives.
Process itself is quite straignforward:

  1. backup your data (not 100 percent neccessary, I did not do it but there are no ciritical files on my NAS, your case might be different).
  2. power off the nas
  3. remove first drive (only, rest stays as it is)
  4. power on the nas, display will say something around the lines of rebuilding RAID, wait for the process to finish
  5. repeat steps 2 to 4 for drives 2,3 and 4
  6. once done, go to dasboard - storage - change raid mode
  7. do not remember exact wording, but there should be option for extending raid to currently unused space, click and wait to finish

Be aware that time to rebuild raid for each drive might be several hours depending of the space used by your files.

Also when selecting new disks, be sure to pick ones without SMR technology, these ■■■■■.

Hello Corwin,

Thank you so much for your reply, and apologies for my very late response - it’s never too late my friend and I’m thankful for your reply. Your method seems very straightforward, so it looks like my solution is to purchase x4 new 6TB drives and change them one by one as you detailed. I thank you for the step by step guide, just what I was hoping for!

The only question I have is relating to Step 6 ‘change Raid mode’ - I take it that this will be Raid 5 once again once the 4 drives have been changed?

Thank you (and the others) for the responses - still nervous as hell about changing the drives but it’s now got to be done!

Best wishes,

Thank you Tech_Wanderer, your response is greatly appreciated. Corwin has responded below with a step by step guide which I intend to follow with the x4 6TB drives you recommend.

Best wishes,

I have a failed drive and thought with that this would be a good time to increase capacity. Do I first need to replace the failed drive with the same size drive or can I buy all larger drives, replace the one in bay 3 and let the RAID 5 get fixed and then replace 1, 2, 4?