Splitting SQL Server tempdb to use a second drive when first drive is full
there a way to put a preference on the SSD drive until full in which case it will resume on the SAN storage?


You can limit the tempdb autogrowth for the primary datafile (that you have on SSD) to 30GB
and then you can create additional datafiles on the SAN.

The drawback will be that you will see imbalance in the tempdb datafile growth.

SQL Server allocates space in a round-robin fashion.

Important Trace flags when dealing with Tempdb :

-T1117 (helps keep data base files equally sized over their lifetime, by triggering all database files in a filegroup for autogrow at the same time.). Note that you wont need this trace flag as you will be eventually restricting the tempdb to NOT grow on SSD once you reach the threshold.

-T1118 (this trace flag switches allocations in tempdb from single-page at a time for the first 8 pages, to immediately allocate an extent (8 pages). It’s used to help alleviate allocation bitmap contention in tempdb under a heavy load of small temp table creation and deletion.) for tempdb.

Refer to Misconceptions around TF 1118 by Paul Randal and SQL Server 2008 Trace Flag -T 1117