If, when attempting to start SQL Server instance, you get an error 1814, this means there's a problem with the tempdb database. Either it can't be created because the disk or volume is not accessible for writing (i.e. a security permission problem), or the volume on which the tempdb resides does not have enough space available. If the latter is the problem, you'll need at least 2 MB of free space for tempdb to be created.
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