> -----Original Message-----
> From: Alex Turner [mailto:[EMAIL PROTECTED]
> Sent: Wednesday, April 20, 2005 12:04 PM
> To: Dave Held
> Cc: pgsql-performance@postgresql.org
> Subject: Re: [PERFORM] How to improve db performance with $7K?
> [...]
> Lets say we invented a new protocol that including the drive telling
> the controller how it was layed out at initialization time so that the
> controller could make better decisions about re-ordering seeks.  It
> would be more cost effective to have that set of electronics just once
> in the controller, than 8 times on each drive in an array, which would
> yield better performance to cost ratio. 

Assuming that a single controller would be able to service 8 drives 
without delays.  The fact that you want the controller to have fairly
intimate knowledge of the drives implies that this is a semi-soft 
solution requiring some fairly fat hardware compared to firmware that is
hard-wired for one drive.  Note that your controller has to be 8x as fast
as the on-board drive firmware.  There's definitely a balance there, and 
it's not entirely clear to me where the break-even point is.

> Therefore I would suggest it is something that should be investigated. 
> After all, why implemented TCQ on each drive, if it can be handled more
> effeciently at the other end by the controller for less money?!

Because it might not cost less. ;)  However, I can see where you might 
want the controller to drive the actual hardware when you have a RAID
setup that requires synchronized seeks, etc.  But in that case, it's 
doing one computation for multiple drives, so there really is a win.

David B. Held
Software Engineer/Array Services Group
200 14th Ave. East,  Sartell, MN 56377
320.534.3637 320.253.7800 800.752.8129

---------------------------(end of broadcast)---------------------------
TIP 4: Don't 'kill -9' the postmaster

Reply via email to