Suggestion to split /data/base directory

Hi postgresql hackers,

I have a suggestion that might improve the performance of
postgresql.
This is regarding the directory structure of /data/base.
The current situation is that every database has one
directory, ie. "mydb", so you will have /data/base/mydb directory.
All the data files, index files, etc are in the same
/data/base/mydb directory.

If I want to split data files and index files to different hardisk, it
is not possible right now.
The only solution right now to improve the performance is to use RAID
method.

My suggestion is to split files into 4 different directories:
/data/base/mydb/data
/data/base/mydb/index
/data/base/mydb/dictionary
/data/base/mydb/tmp

So I can put each directory on different hardisk, so I can
have 4 hardisks for 'mydb' database.

Is it doable and a good idea?

Regards,
Chai