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Have you ever come across such kind of case that the Raid is out of space? Generally, the purpose of expanding Raid 5 partition is to maximize the performance of server computers by having more disk space on Raid 5.
Unless the highpoint controller which supports a Raid expansion feature,there isn't any direct method for you to expand Raid 5 array.
The only other way is to first backup data on Raid 5. Then delete the 3 drive array and re-create it as a 4 drive array. Restore the data to the new larger Raid 5 array.
Note: If you add a disk that's larger than the other disks, it will be resized to match the capacity of the others. In other words, if you have three 80 GB disks and add a 160 GB disk you will only be able to use 80 GB of the 160 in your new configuration. The rest of capacity of the drive will be unusable.
Here, we would like to provide solutions for both two conditions that you may come across to expand the Raid 5 array:
Firstly, if your Raid controller supports a Raid array expansion feature, it is more convenient and easy with third party Raid array partition software. Insert a new hard disk to the existing hardware Raid and organize this Raid using Raid controller. Then there is some unallocated space on this Raid. Install the Raid partition software and then resize the Raid partition with the unallocated space. For more details, please refer to: How to resize/extend Raid 5 array in a safe way?
Secondly, if your Raid controller doesn't support a Raid expansion feature, the only but safest way to extend Raid 5 array is to backup all data to a safe place, like an external hard drive and then break the Raid array, connect the new disk to computer and recombine the Raid 5 array by using the Raid controller with all the disks you want to utilize. Here we recommend you to use Raid 5 copy software.