Replace hard disk with bad sector, file system missing

Your actions have made you RAID array "inactive", so it no longer appears in the WebUI and the associated filesystem cannot be mounted and so is shown as "missing" in the WebUI. You need to reverse what you have done and then follow the correct procedure outlined below.

Shutdown and put the faulty drive back in your machine, making a note of the drive's serial number. If you have enough SATA ports you can leave the new one in place, otherwise you'll have to remove the new drive. On restarting your machine, your array should return to its previous state with the defective drive in place.

To Replace a drive in the array do the following:

1. Using WebUI to identify the device letter of the defective drive by checking SMART data and cross checking serial number on the listed disks.

2. Using the "Multiple Device" tab, use the "remove" option to select the defective drive to remove it from the array - save & apply this change.

3. The array status should now change to "clean, degraded".

Shutdown machine (if necessary) to physically replace the defective drive, making a note of the new drive's serial number.

4. Use the WebUI to identify the device letter of the new drive.

5. Using the "Multiple Device" tab, use the "recover" option to select the new drive to add it to the array - save & apply this change.

6. The array status should now change to clean and be resyncing.

Quote from leozora

I tried the steps and the raid becomes degraded and I can replace the disk.

The problem, however, is that now one of the disks has a warning in the S.M.A.R.T. state, but if it breaks, how can I not see the RAID in a degraded state?

Have you replaced the faulty disk?

If yes, do you now have a SMART warning on another disk? RAID will not show as degraded unless a disk totally fails or a disk is removed from the via the WebUI.

If the array details are no longer visible in the WEBUI it's probably in an "inactive state" which you can confirm at the CLI by usingcat /proc/mdstat.

For example:

root@omvt:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]  
md0 : inactive sdd[3](S)

     10478080 blocks super 1.2


unused devices: <none>
root@omvt:~#

Depending on the state of the disks that were in the array you may need to re-assemble or re-create it. If you end up with an inactive array the simplest thing to do is to ask for guidance on this forum.