SQL Server Rollback being performed - how to stop it?
@MaxVernon already gave  all the info you need. Just some addition from my side. The bigger the transaction the harder the (pre)calculation for the SQL Server. That's why your remaining time in seconds may increase while the process runs. After running a query the SQL Server can't grant more memory to the process. For big calculations your tempdb will most probably be used. And yes this will lead to a disk intensive call.  That's why it's nearly always best to keep the transactions small. 

Also please note that restarting SQL Server is in most cases a bad idea, since it has multiple negative side effects. It will for example rebuild the TEMP DB and also clear statistics...
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