What are LooksAlive” and IsAlive” checks?

[Nicholas]

Hi, I would like to ask you a big question about my situation, what are “looksalive” and “isalive” checks? Thank you please help me quickly because I'm stressed.

[Ciaran]

When an instance of SQL Server is running in a Clustered Environment, Microsoft Cluster Service performs two checks to confirm if the SQL Server resource is still available. One is LooksAlive and the other one is IsAlive check.

LooksAlive is a basic check in which the Cluster service queries the Windows Service Control Manager to check if the SQL Server service is still running. By default this check happens every 5 seconds. During IsAlive check the Cluster Service connects to the SQL Server instance with the help of c:\windows\system32\sqsrvres.dll and runs SELECT @@SERVERNAME against the instance. This check does not check if the user databases are online or not. It just checks the SQL Server instance availability. This check happens every 60 seconds by default.