[Dovecot] Maildir feature I'd like to see - SSD for newer messages

[Marc Perkel]

On 12/23/2010 11:37 AM, Javier de Miguel Rodríguez wrote:
> On Thu, 23 Dec 2010 11:27:45 -0800, Marc Perkel <marc at perkel.com> wrote:
>> SSD drives are very fast but expensive. So I have a crude idea that
>> I'd like to see. May not be practical but would like to get some
>> thoughts on it.
>
>
> You are asking about automatic storage tiering. You can get what you 
> want in a transparant way, independient
> of Dovecot. Some storage vendor (search for Fully Automated Storage 
> Tiering - FAST from EMC or Compellent, recently
> bought by Dell) get what you are asking for.
>
> If the budget is low, you can achive a "poor´s man" storage tiering 
> with some shell scripting, cron and soft links; Or you can look at 
> http://code.google.com/p/fscops/ for a more mature implementation. Or 
> just use ZFS and "hybrid storage pools"
>
>

I wonder if there's any way to do this. Say there are two different 
storage devices mounted as follows:

/slow-hard-drive/email-directory
/fast-ssd-drive/email-directory

Now suppose there were a way to join these drives so that you could 
access them as a single directory:

/joined-drive/email-directory

The Dovecot could see the joined drive but my backup/archiving scripts 
could see the drives independently and move old data from the fast 
drives to the slow drives.

I think back in the old DOS days you could do that. Is there a way in 
Linux to do the same thing? Join two directories so as to make them look 
like one?