Len,

Begging to differ, as is my wont...

>wastes main CPU mips.

I understand that you're getting at the offloading of certain tasks to
I/O  processors,  but RAM drives will still blow 'em out of the water.
The  higher  CPU  cost  is  a  non-issue,  as the reads and writes are
completed  much,  much  faster.  And much of what the I/O processor is
great   at   offloading--RAID  computation,  cache  management,  event
logging, etc.--aren't even needed at all for dynamic data.

For RAM drives to perform optimally, the RAM bus in the machine should
be  SDRAM  or  DDR. Mission-critical data such as user mailboxes still
needs  to  be on a high-powered RAID card, so it's not like I'm saying
they're outmoded!

>Do  this  at least for the IMail spool+log directory, which is really
>where the read/write traffic jam is worst.

Web  Messaging  is  where  the traffic jam is at its worst, due to its
reliance  on  the  swapfile. Put the swapfile in RAM and watch it blow
you away. There's no better way to argue it.

>There�s  a  good  probability that an incoming SMTP messaging will be
>written to the cache...without ever touching the spool disk.

On  an  unloaded system, a very good chance. With Web Messaging backed
by  a  huge,  constantly  changing swapfile, a *lot* less of a chance.
(Unless  you've  got  multiple  RAID  cards/caches, which'll help, but
still isn't going to beat running from RAM.)

Sandy


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