There is no one answer fits all as it changes from manufacturer to manufacturer.

If I was you, get some storage somewhere - ideally (for speed) use an external hard drive but anything will do and make a full backup of everything.

Once you have a backup, try simply changing the faulty hard drive.

Some will just automatically rebuild whilst others may say foreign/unrecognised disk and require you to enter the Raid Setup then manually extend the existing Raid to it.

There is no way for any of us to know without more information, but as long as you are careful, you should not loose the existing data on the good hard drive - but we can not say for sure, and again, you should take a backup just in case.

There is no one answer fits all as it changes from manufacturer to manufacturer.

If I was you, get some storage somewhere - ideally (for speed) use an external hard drive but anything will do and make a full backup of everything.

Once you have a backup, try simply changing the faulty hard drive.

Some will just automatically rebuild whilst others may say foreign/unrecognised disk and require you to enter the RAID Setup then manually extend the existing RAID to it.

There is no way for any of us to know without more information, but as long as you are careful, you should not lose the existing data on the good hard drive - but we can not say for sure, and again, you should take a backup just in case.