How will RAID 1 behave?

Question

System administration

Good day. Such a situation:
There is a Dell PowerEDGE 1950 III server with two Seagate ST3500620SS 500Gb SAS screws in the first raid (mirror). There were a lot of things on the screws (database + archives), all data is critical, that is, constant access is needed, even in the middle of the night. (do not ask why I can hardly understand, but such is the situation) Backup for certain reasons was not done and cannot be done.
So, one of the screws flew out. There are no such screws in quick access. As an option, we are thinking of replacing it with a Seagate 3.5" 1TB SAS 7200rpm 64MB Constellation ES (ST1000NM0001), but here's how we plan to do it so as not to interrupt the workflow. Insert one new screw instead of the old one and transfer all the information from the old working screw to the new one and, of course, boot from it, then plug in a second new one and combine them into the first raid. It seems that everything is fine, but you will have to reboot the server for a while, which is fraught. As an option, we consider such a case to simply insert a new screw into the server and try to raise the RAID 1 so that the information signed up for a new screw, then pull out the old one and insert a second new one, but the screws are slightly different both in volume and firmware, respectively, irreparable things can happen.
The bottom line is that there are no these screws, you have to buy them, and I would like to be more or less sure that the circuit will work.
What do you say, what do you recommend?
Z.Y. On the server is FreeBSD, raid controller Dell PERC 6 LSI Logic SAS1078.

Answer 1

Without backups, your operations are like shooting yourself in the foot, there is certainly a chance that you will miss, but it is much more likely that you will shoot yourself in the foot.

Answer 2

The correct algorithm
is to back up all the data;
- replace the failed HDD, go to the raid settings, make it hotspare for this array, wait for the rebuild to finish.
- if you want, then similarly replace the second HDD;
- if "everything is lost, boss", then restore from the backup.

Answer 3

backup - new raid - deploy backup. This is if the data on the server is really important
. And if not, all methods are approximately equally "useful" =)