RE: Single-level storage

Yep, was talking about iSeries.

Say the box has 256 GB of RAM and a 4-disk raid 5 set of 70 GB drives.
That would give you 210 GB of usable disk.  There's no way that you'd
ever exceed the amount of ram, and it would give you 46 GB of "temp"
space to swap in/out logfiles or other extraneous junk.

Just a hypothetical... But it was my understanding that with
single-level storage on the iSeries, the system sees RAM and DASD as the
same and if you request something from disk, it pulls it in to memory
until something else kicks it out.  But if you have more main storage
than disk, it shouldn't ever get booted (with exception of logs and temp
and whatnot).

By no means do I want to do this, I was just thinking about it.
Besides, the days of high-speed chip-based DASD are coming within the
next 10-20 years.  We'll google this discussion in 2026 and laugh!


--
Justin C. Haase - iSeries System Engineer
IBM Certified Systems Expert - System i
Kingland Systems Corporation

-----Original Message-----
From: midrange-l-bounces+justin.haase=kingland.com@xxxxxxxxxxxx
[mailto:midrange-l-bounces+justin.haase=kingland.com@xxxxxxxxxxxx] On
Behalf Of Jones, John (US)
Sent: Thursday, August 24, 2006 11:11 AM
To: Midrange Systems Technical Discussion
Subject: RE: Single-level storage

Assuming you're talking about an iSeries and ignoring the lack of
cost-effectiveness of such a machine...

Writes are going to be flushed to disk either immediately or within a
few seconds depending on how it's set up. Main storage to DASD
controller cache to disk drives.  And you want that, too, to ensure data
is safely stored and to shorten the power-down RAM flush cycle.  After
all if you have a hard stop on the machine for some reason you don't
want to lose all of your production updates.

(The writes may be data but will also include spool files, message
queues, system history logs, journals, etc.)

The nice thing is that the writes won't slow system performance to any
noticeable degree.  The vast majority of the write activity will
basically be behind the scenes and take idle cycles or co-processors.

BTW, assuming upon startup you do a SETOBJACC on everything to
front-load in to RAM things will take a while -- maybe a long while --
to get going.


Now, on a Windows PC the problem is substantially the same: At some
point writes are done as file contents, event logs, etc. are changed as
part of a normal running system.  If you have a lot more RAM than needed
you could set up a RAM disk to eliminate some of the physical disk I/O.
Also, Windows will always use the swap file even when sufficient RAM
exists to avoid it.  Turning off the swap file in my experience has
always led to an unstable system.

John A. Jones, CISSP
Americas Information Security Officer
Jones Lang LaSalle, Inc.
V: +1-630-455-2787 F: +1-312-601-1782
john.jones@xxxxxxxxxx

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Haase, Justin C.
Sent: Thursday, August 24, 2006 10:26 AM
To: Midrange Systems Technical Discussion
Subject: Single-level storage

Noodle on this one.

If a system had equal or more main storage than attached DASD, would the
only disk activity be read operations until a shutdown when the system
would dump what's in main storage to disk?

--
Justin C. Haase - iSeries System Engineer IBM Certified Systems Expert -
System i Kingland Systems Corporation


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