According to BOL , a database in SUSPECT state is : “At least the primary filegroup is suspect and may be damaged. The database cannot be recovered during startup of SQL Server. The database is unavailable. Additional action by the user is required to resolve the problem”

 There are numerous reasons for a SQL Server database to be marked SUSPECT.  A  suitable and tightly monitored database backup strategy is critical.

Some common causes

1. Missing device when SQL Server starts

2. Denial of access to a database resource by the operating system

3. A drive where log files reside goes offline.

4. Anti-virus or 3rd party software blocking access

5.  Killing a DBCC comand : Failure of rollback of big job and renaming db,  e.g  a developer  is performing cleanup of a  database realised that it brings your server on its knees, the developer stops a job which starts rollback and it takes forever

6 . A  hardware/ network issue. Needs investigation and  can be difficult to find.

7. Corruption of database file(s)

Actions to take if a database in SUSPECT status:

1)                  Don’t reset status immediately, start a restore or any other change that is difficult to reverse.

2)                  Check Logs for relevant messages. Quite often they are unavailable, so consider some remedial action

3)                  Contact DBA and propose a) a server restart b) change to emergency mode where copies can be taken

4)                  If a suitable BACKUP is available enact a RESTORE procedure.

5)                  Test RESTORE procedure regularly to ensure integrity