Need PRM Disk Bandwidth HOWTO

[Andrew Underhill]

Help. I've got PRM 2.01 with all the patches that I could track down, on a system running hp-ux 11.11, and am having a problem configuring (and problably understanding) the PRM Disk Bandwidth Manager.

When I use XPRM to configure the disk bandwidth for a VxVM Disk Group, I select the DG (and the Volume Group box is then populated with the name of the DG), but the Group box remains greyed and uneditable), so setting the shares doesn't work (the modify button does not ungrey).

If no DG is selected, and "Add all missing" is pressed a message"User Error/The fields "Volume Group is required. Please enter a value". This is the case even when a DG is selected.

So the question is considering that this system is patched to the hilt what is missing or what am I doing wrong?

Also does the disk bandwidth manager manage bandwidth globally, or on a per DG basis? I.E are the shares for a DG just for that group on the DG or for that group on that DG in the whole system? The manual is a bit skimpy on the Disk Bandwidth subject.

Thanks in advance

[melvyn burnard]

What version of VxVM are you using?
PRM only supports VxVM 3.5 and above, and does have a patch requirement.
Please see the Release Notes at:
http://docs.hp.com/hpux/pdf/B3947-90029.pdf

[Andrew Underhill]

Thanks,

VxVM 3.5, and I've been through the document and applied those patches.

I've now experimented with editing /etc/prmconf directly as although I was using the gui because I was uncertain of how/what to do, I need to progress this problem.

Can you enlighten me as to how PRM controls access to disks? If I give a group shares that are equivalent to say 80% to a DG how is that balanced with other groups accessing other DGs.

TIA

[Jonathan Fears]

First I'll answer the question you had about xprm. The Group box under the DiskBandwidth tab is always grayed out. This is xprm's way of ensuring there is always a 1-to-1 ratio kept between disk-bandwidth records per DG and group/CPU records. The order of operations for entering disk records through xprm should be:

1) select the disk group from the pull-down tab
2) select "Add all missing" button
To change allocation for groups, expand the DG in the left pane
3) select the PRM group, then change its allocation in the right pane

Second, PRM manages disk bandwidth on a per DG basis. PRM re-organizes a disk group's I/O requests based on the allocations you have given in the configuration file. In other words, the larger the allocation a group is given, the higher and more often it is placed in the DG's run queue.

[Andrew Underhill]

Thanks.

Just to clarify:

Group A has 100 shares to DG1
Group B has 120 shares to DG1
Group C has 100 shares to DG2

DG1 which is used by App1 has a higher priority than DG2 because Group A+B > Group C?

Is this correct? Or is it merely that B>(A & C) and that's it.

The reason why I ask is that each App with have its own DG, and will have its own set of user, i.e. Group. Consequently the first scenario is what I need, but the latter is fairly pointless for me.

Thanks

[Jonathan Fears · Accepted solution]

As I said in the previous post, for every DG in the config file there must be a 1-to-1 ratio between it and the PRM groups. Take for example the configuration below:

OTHERS:1:50::
prmgrp2:2:50::
prmgrp3:3:50::

/dev/vgprm01:1:1::
/dev/vgprm01:2:50::
/dev/vgprm01:3:50::
/dev/vgprm02:1:1::
/dev/vgprm02:2:20::
/dev/vgprm02:3:80::

We see on /dev/vg01, the two user-defined PRM groups are equally important and therefore are given entitlements allowing them equal access to the volume group. On /dev/vg02 however, say prmgrp3 is running some important databases and therefore should have more access to the disk than prmgrp2 which may be contain some other non-critical apps.

One note though, you only need disk bandwidth controls when you have multiple PRM groups competing for bandwidth on the same DG. If each PRM group has its own DG as you stated, the disk bandwith records will have no effect.