I know you're in the middle of some other issues at the moment, but when
you get back to it heres my 2 cents:
Even with PAV devices on a mod-27, you will still be using Linux Processor
cycles to start more than one I/O per volume. VM will have to directly
attach the PAV devices to the Linux guest and the Linux guest will have to
run dm-multipath to treat all those devices ( Base and Aliases ) as a
single volume.
So no - there is no CPU savings using PAV, but probably provides an I/O
throughput benifit at the cost of some CPU. I say probably because I've
not actually measured the difference.
One of these days in my copious spare time, I'd like to measure the actual
CPU costs of using dm-multipath & PAV on -9s vs lots of -3s
While I'm here - I'd like to second Alan's suggestion regarding the DOS
attack. The best place to handle a DOS attack is in the network
infrastructure outside the processor.
Jay Brenneman
Tom Duerbusch
<[EMAIL PROTECTED]
iscity.com> To
Sent by: Linux on [email protected]
390 Port cc
<[EMAIL PROTECTED]
IST.EDU> Subject
PAV vs LVM vs native
06/07/2005 11:00
Please respond to
Linux on 390 Port
Sorry about the length of this...
I will be running Oracle 10g (64 bit), under SLES9, under z/VM 5.1 on a
z/890 with a ficon attached Shark.
I have some large databases that I will need to configure.
One database will be used for a single application.
The other database will be used for multiple (15-20) applications.
For now, the data portion of the database will be either:
10 3390 mod 27s or
30 3390 mod 9s or
90 3390 mod 3s
That is suppose to all come out to basically the same size.
So, I'm trying to make an informed decision on what will be best (or
best for us).
Assuming that device addresses are not a concern (i.e. that the 255
device limit per Shark LSS isn't going to be a problem) what are the
pros and cons of each of the following?
PAV: Is hardware supported.
It seems that I can't define a full pack minidisk on it, but will have
to attach the PAV to the Linux machine...no MDC for these volumes. I
may still do LVM of the 10 volumes to present a single image to Oracle,
or not.
Is there CPU savings in using hardware supported PAV, vs Linux
supported LVM? Any other savings or limitations?
LVM: Linux supported.
May take more CPU cycles then the hardware option. May be used in
conjunction with PAV to give a single volume image. May need to use the
expanded device names (/dev/dasda1 to /dasdz1 just isn't going to cut
it).
Oracle supported:
You can give any number (within reason) of disks to Oracle which can
use them as a single pool of space. Since all of this space is going to
Oracle anyway, management of 90 volumes vs 10 volumes shouldn't be a big
concern. There may be some advantage for Oracle to be able to manage
multiple disks vs letting the hardware or OS handle it for you.
Right now, I'm torn between hardware supported PAV (hardware using less
CPU cycles to manage..right?) and Oracle supported. With a single LVM
image, will Oracle try to do only 1 I/O at a time?
I expect the data to be cache unfriendly. We can't afford the money
for either an increase in Shark cache or to increase the Oracle SGA to
make sure we have a high cache hit ratio. But I expect our total I/O
rate for these two Oracle databases to be in the 1,000 to 2,000 I/O per
second in the worst case.
The Shark has 8 8 pack pairs of 72 GB disks at 15K RPM and 8 GB of
cache.
Is there a difference in the considerations between an Oracle database
that supports one application (i.e. large tables) vs an Oracle database
that supports many applications (smaller tables but 20 times as many)?
Tom Duerbusch
THD Consulting
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