Re: Single-level storage

On 8/24/06, Haase, Justin C. <justin.haase@xxxxxxxxxxxx> wrote:

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).

this post by Hans Boldt from a few years back does a good job putting
the SLS in perspective:

http://archive.midrange.com/midrange-l/200304/msg01508.html

It is CL, commands and the object oriented encapsulation of system
objects that makes i5/OS so easy to work with.   Ironically, if you
read between the lines in Hans's post, SLS might be the thing that has
prevented IBM from marketing i5/OS to a broader audience.

"...What OS/400 adds to that is the concept of single level store, in
which the persistent store (hard disks) is basically considered one
big swap file. ..."

"...Let's compare this to the typical system design. In other
operating systems, an address normally only refers to the space
assigned to a particular process. Processes, therefore, are then
prevented from accessing storage belonging to other processes. On the
other hand, in a single level store architecture, since a pointer can
point anywhere within the entire address space, not only must the
pointer have more bits for the address, but the pointer must also
contain permission information to prevent the pointer from being used
to access (or worse, change) storage it has no business to. Thus, the
16 *byte* pointer. ..."

"...OK, so we've had a commercial implementation of single level store
for 25 years now, and the concept was certainly known before that. (I
learned about it in my operating systems course in the late 70's.) But
have you ever noticed that no other computer manufacturer offers an
operating system with single level store? ..."

"...What's my point in all this? Single level store is certainly an
interesting idea. But in my opinion, it's not really that significant
a factor in the success of the AS/400 and iSeries. And because of it's
heavy resource requirements, it may have been a limiting factor,
especially in the days of the S/38. But then who knows where we would
be today if the S/38 had been designed with a more conventional
architecture? ..."