Corruption on MS SQL Database due to 1 failed disk on RAID 6 Why is that when a single disk fails from a RAID 6 setup MS SQL 2014 database corrupts with the following error:

DESCRIPTION:    SQL Server detected a logical consistency-based I/O error: torn page (expected signature: 0x55555555; actual signature: 0xad191b0d). It occurred during a read of page (1:144366313) in database ID 19 at offset 0x0001135b5d2000 in file 'D:\MSSQL12.LIST133\MSSQL\DATA\test.mdf'.  Additional messages in the SQL Server error log or system event log may provide more detail. This is a severe error condition that threatens database integrity and must be corrected immediately. Complete a full database consistency check (DBCC CHECKDB). This error can be caused by many factors; for more information, see SQL Server Books Online.

The RAID 6 status is healthy and hasn't change even with one disk failed (the issue should appear when 3 DISKs fail). How does the SQL knows what is going on with the DISK since it is not a software RAID 6? There is a seperate controller and a storage.
Also what is the point of having spare disks in the RAID  if the SQL is going to corrupt anyway? How can I avoid this?
Firstly you should change your database page verification setting from tornpage to checksum to have more reliable identification of database corruption.
secondly SQL Server has detected an I/O error - not surprising if an entire disk failed (or was removed while you tested your test db). - Anyway you won't know if the database is corrupt until you complete the recommended action - DBCC CHECKDB