PostgreSQL: Table and index on different tablespace

Like this:

create table THIS_TABLE (
  id number NOT NULL, 
  constraint THIS_TABLE_PK PRIMARY KEY(id) 
             USING INDEX TABLESPACE INDEX_TABLESPACE
) tablespace DATA_TABLESPACE;

USING INDEX TABLESPACE is the syntax - you weren't far off.

As far as good/bad practice is concerned, that's opinion-based, so not really something that should be asked here. The alternative is to use the ALTER TABLE .... syntax after table creation.

How much improvement are you expecting from the SSD? It is surprising how little physical I/O actually happens on busy indexes and I don't think I've ever solved an actual performance problem with physical I/O devices.

I don't know enough about PostgresSQL to comment on buffering or recoverability and the like but I will say that choosing performance over recoverability is probably not a good practice.

I never want to find out that I have found a previously unknown recovery bug when my data is sitting in a tape on a shelf. I learned the DBA craft in the days before RAID - every night was a sleepless night. Always, always, always use RAID's.

If a user is complaining about performance, tell them you need a dozen SSD's to put in a 10 disk RAID5 array with hot failover. He'll leave with his head spinning but he might come back with a purchase order.

Good luck.