HP DL380 G6 running Rocky Linux 8 with two sets of 4 HDDs in RAID 5. Lets call them A and B.
Just got some larger drives, C, to replace the ones which currently have OS, A. The second set of 4 drivers, B, currently doesn’t have anything I can’t remove.
What’s the simplest way to switch my smaller OS drives, A, with the new ones? Can I just hot swap them one at a time then do a new partition for the new larger space? Or should I remove the B drives and then copy everything from A onto the new drives C, then put the B drives in the slots A was in?
I wouldn’t hot swap unless up time is important to you, I’d shut down, replace one of the drives, rebuild the array with the new drive, shut down, replace other drive, rebuild then extend.
The advantage of doing cold swaps is you know that you have a clean and working image on the drive you remove, so if anything goes wrong you can roll back there. If you hot swap the drives potentially the data on the drive you pull will be corrupted.
Can I just power down, replace 1 drive, power on and let it set up the new drive automatically (and repeat for each HDD) or do I need to use a tool to re-build the array with the new drive?
Having upgraded several RAID-5 arrays over time I used Webmin to control the array. First I swapped the drives physically, then told Webmin to remove the missing drive from the array, then add the new drive to the array. Wait for rebuild, rinse, repeat. The waiting to rebuild time is the worst, as the array is the most vulnerable for data loss.
For your use-case, I’d suggest copying the OS data from the array to a new temp-disk, delete array A entirely, install the new disks and create a new array A, reinstall the OS, then copy relevant parts of the OS back to array A from the temp disk. This allows you to refresh the OS and complete the upgrade in the shortest possible time with the least chance of data loss.
Sorry, I think my phone might have cut off some of your initial post or I simply misread as I was under the impression you were using RAID 1 for your OS.
RAID 5 there is no real advantage to the cold shutdown I suggested, and you’re also unlikely to be able to grow the array after the fact.
As such best approach will be to backup array A, shutdown and swap out all four drives, create new larger raid 5 array on new drives and restore to that array from backup.
If anything goes wrong, put the original 4 drives back in and try taking another backup/changing approach.