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Mixed HDD sized using Raid5 and mdadm

cm flag

I currently have three 4TB HDDs in a raid 5 array using mdadm on Ubuntu 23.04. I only have 2 HDD open slots left. I am thinking about adding two 18TB HDD to my PC. Then combing the three 4 TB drives as a single volume resulting in 12 TB. Then making a 3 member Raid 5 out of the two 18TB HDD + the 12 TB volume. I know that will waste 6 TB on each of the two 18 TB HDD. That would result in 24 TB of usable raid 5 storage.

My two questions are:

  1. if I go the route above and then next time I need additional storage, I remove the three 4TB drives in the volume from the raid 5 set and replace that with a 18 TB HDD, will the resulting storage be the same 24TB (three 12TB in raid 5) or will it increase to 36TB (three 18TB in raid 5)?

  2. With that approach is it possible to keep the data on the drives and not re-partition or format the HDD. I don't have enough free storage to backup the 24TB raid 5, so was hoping the "grow" option would do what I need.

I am trying to create a strategy that will delay buying a third 18TB HDD now knowing that it will be cheaper when I need it in a year or two.

Terrance avatar
id flag
This will probably have the best information for you to help you. But your thoughts are good in what you can do. You are definitely on the right track. https://raid.wiki.kernel.org/index.php/Growing But, when it comes to messing with partitions, nothing is ever guaranteed. Always best to have backups of your most important stuff that you cannot lose.
SkiBum avatar
cm flag
Very useful link! Thank you!
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