It is running since 20 hours....Any idea why it is taking so long and why it is not completed yet?
Maybe because there is corruption.
The checkDB algorithms are written in such a way that they can tell quickly if there is corruption or not, but if there is, then SQL has to go back and do extra detailed searches. it's called a 'deep-dive' and it can make the CheckDB time go up massively.
Wait until it's finished. To tell what's wrong we need the results. If you stop it now you're just going to have to run it to completion later.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
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