I am currently doing a project to migrate the SQL servers.
The old SQL server database has 4.0gb database size and 1.5gb log size, and I found out that the actual data is only 1.7gb. So I made new database 3.0gb and 800mb log.

I did an inital testing that is to leave the current system on line and scheduled an database/object transfer task at night. It worked fine, and I check the transaction log was only used 0.25 mb. I used DBCC checktable(syslogs). Does SQL Server automatically issue the DUMP TRAN command after DATABASE/OBJECT TRANSFER finishs.

When time comes to do a real transfer. I stopped all the backup job, and made the database at DBO Only mode. However, after almost two hours transfer, SQL server gives me the error message 1105, transaction log runs out space.

My questions is : Why it worked ok at the testing? The period of time between testing and a real transfer only one night, so the database size is almost the same? I have done three times already, every time increasing the log size by 100mb, it keeps happening again, so my last bet is to make the log device size the same as the old one, 1.5gb.