RE: Disk: Percent full a performance factor?

I did suggest disk busy had to be in range as well...... With the hosted
disk the disk busy on the primary (hosting) LPAR is going to be minimal. On
a box with heavy index creation, yikes......

--
Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of
DrFranken
Sent: Monday, October 20, 2014 2:49 PM
To: Midrange Systems Technical Discussion
Subject: Re: Disk: Percent full a performance factor?

Yes BUT. Fragmentation will begin to create issues.

The reason % busy can climb when disks fill is that instead of just driving
the car into the garage you must first remove the wheels the front and rear
bumpers and put them into the garage. Then lower the drop top and tip it on
it's side on a cart and slip it in the available space. Yes the trip to work
tomorrow is gonna suck too as you have to undo this effort to drive it
again.

So enough arms as Jim suggests helps with this but extra effort is still
required it's just hidden by extra capacity. If that's OK in your shop good
for you. (Really!) But if you're pushing the %busy to a point where those
extra I/Os hit knee of curve then that's bad.

It makes a HUGE difference what sort of I/O you are doing. If it's causing
the data to move about with sorting and index builds and reorgs and restores
and copies then this will matter much more to you as fragmentation will be
far worse with that activity.

On the flip side I have customers with IBM i 7.1 as a host partition with
nothing but NWSSTG filling the disk to 95%. They have been that way for over
a year and a half with no issue whatever because those things are written to
their full size when built and never move. The I/O is just within them.


- Larry "DrFranken" Bolhuis

www.frankeni.com
www.iDevCloud.com
www.iInTheCloud.com

On 10/20/2014 2:53 PM, Jim Oberholtzer wrote:

Rob,

It depends on how many DASD devices there are. If there are say 40-50
devices then running up to 85% -- 88% might not be a problem, but with
6 devices, you're in for a hard time.

Generally Databases tell you the knee in the response time curve starts at
about 80% and steepens quickly but with IBM i, as long as the DASD

device

busy percentages are OK and there is room for temporary indexes, then
that percent full you have to be concerned with goes up as well, so
higher percent full is OK.

--
Jim Oberholtzer
Chief Technical Architect
Agile Technology Architects


-----Original Message-----
From: MIDRANGE-L [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of
rob@xxxxxxxxx
Sent: Monday, October 20, 2014 1:29 PM
To: midrange-l@xxxxxxxxxxxx
Subject: Disk: Percent full a performance factor?

The old rule of thumb I had learned back on the S/36 was that you
really didn't want to go over 80% of disk space used. I had a manager
(came from the programmer pit and rose through the ranks) that
wondered if that still held true with the growth of disk. After all,
20% free of a whole gig of disk space sure was a lot more than 20% of
300MB. I argued that object size was significantly larger and that
reorgs and whatnot still needed significant portions of disk space.
Now that we're measuring disk in TB and MB is nought but a rounding
error does 80% still hold true? If so, why?


Rob Berendt
--
IBM Certified System Administrator - IBM i 6.1 Group Dekko Dept 1600
Mail
to: 2505 Dekko Drive
Garrett, IN 46738
Ship to: Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com

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