I have a storage subsystem which allows five independant RAID 10 devices. I am creating five filegroups each with 2 data files distributed across the devices in a smart round robin fashion.
I have assigned tables which are commonly joined between the filegroups. For example, Table A is in Filegroup 1 while Table B is in Filegroup 2. The most common and high volume query is the join between these two tables.
My question is this: I understand SQL Server is theaded by data file, not filegroup. But for filegroups which have 2 or more data files, do they both grow evenly? Or once one data file is full, SQL Server then writes all new data to the new data file in the same filegroup.
SQL Server will write data to the members of a filegroup evenly, so if you create 2 100MB files in a filegroup, then insert 150MB of data into this filegroup, you will have 75 MB in each. Figuring out what you have after you delete 80 MB of data is virtually impossible, however. Hope this helps.