Lane asks:
> In the "old" days I was always told to change the maximum
> permanent space to 100% on all drives except ldev 1. Is this'
> still valid? Is there a down side to leaving it at the default
> of 75%? Well other then unusable disk space, but with drives
> as cheap as they are these days I'm not all that worried.

The advice is probably as valid today as it ever was.  Obviously you don't
want to run out of transient space (I assume this results in a System Abort,
but this certainly hasn't been a common problem in my experience).

Increasing the Permanent% on non-LDEV 1 disks from its default of 75% is a
great trick for a customer who has run out of space as you make more disk
storage appear as magic from out of nowhere (especially on really big disk
drives where 25% adds up to a heck of a lot of space).

If you've got a very large number of users, you might want to make sure that
the absolute amount of space reserved for transient space is something
reasonable.  Note that the maximum "percentage" values are just that
(percentages), so the actual amount of space represented will vary based on
the size of each disk.

Determining what's "reasonable" can probably be done by monitoring the
amount of transient space in use when the system has a lot of
users/connections/jobs.

Increasing the Permanent% won't reduce the amount of space available to
transient space until you actually use up that "new" permanent space.

Decreasing the Permanent% can be a nice way to hide disk space if your site
tends to run out of it all the time.  If you need it you can instantly make
it available by changing the Permanent% up in VOLUTIL.  You can probably
also use this as a tool to help balance disk usage.

The maximum Permanent% allowed on LDEV 1 varies by device size.  If you're
trying to squeeze out the last byte of free space (say on a development
machine with only one disk) you can keep trying higher Permanent% values
until you get an error (usually somewhere between 85-95% IIRC).

G.