meaning of quorum more

[DENNY JOSEPH_1]

we are using hpux -lq for booting in quorum mode, actually what is the meaning of quorum mode.

[Patrick Wallek · Accepted solution]

'-lq' actually mean "low quorum" mode. This allows the system to boot even in there is NOT a quorum of disks available.

Basically if you have 2 disks mirrored in VG00 and 1 fails, you no longer have a quorum of disks. Using 'hpux -lq' to boot allows the system to boot anyway.

A quorum, in disk terms, is defined as 50% of the disks plus 1.

So, if you have 2 disks, 50% of 2 is 1, and 1 + 1 is 2. If one disks fails you can never have a quorum.

If you have 4 disks, 50% of 4 is 2, and 2 + 1 is 3, so a quorum in that case is 3 disks.

Hopefully this is clear.

[Steven Schweda]

> A quorum, in disk terms, is defined as 50%
> of the disks plus 1.

So, if you have 3 disks, 50% of 3 is 1.5, and
1.5 + 1 is 2.5? What's half a disk look
like?

"More than half" might be a simpler
formulation.

[VK2COT]

Hello,

There are several quorum definitions on
HP-UX.

a) For LVM volume groups, there are two
types of quorum:

Activation quorum
Running quorum

Activation quorum applies when the VG is
activated, and requires at least 50% of the
disks that were in the VG at the end of its
last activation are present. The important
note is that it is based on how many PVs
were left in the VG at the end of the
activation.

Running quorum determines what happens when
a PV fails whilst the VG is activated, and
requires that 50% or more of the PVs
available in the VG at the time remain
available. You can not override running quorum!

b) And there is ServiceGuard quorum.
But that is not part of your question :)

Cheers,

VK2COT

[Steven Schweda]

> [...] at least 50% [...]

> [...] 50% or more [...]

These differ from "more than half". Which do
you think is correct?

[VK2COT]

Hello,

> [...] at least 50% [...]

> [...] 50% or more [...]

> These differ from "more than half". Which do
> you think is correct?

Both. For running quorum, one can lose a
disk in a two-PV scenario and it will still work fine! And that is exactly 50% quorum
satisfaction.

Again, there are two distinct quorum
figures (for different needs).

Cheers,

VK2COT

[VK2COT]

And come to think about the English language
a bit more...

"at least 50%" should probably be "at least 51%"

One day I will tell you the story how
I failed my first job interview as a new
migrant in Australia in 1990 when I used
word "gay" to describe my happy character.
The British classics used that word with
different meaning to what it is today.
I lost job offer because of it (although happily married with two kids).

English language is always a mystery :)

VK2COT

[Steven Schweda]

> And come to think about the English
> language a bit more...

The problem is not in English, it's in math.
">=" and ">" are different.

> "at least 50%" should probably be "at least
> 51%"

Not really. "More than" works just fine in
this situation. "At least" does not. (And
with 500 disks, "51%" is not what you need.)

> English language is always a mystery :)

Well, often.

[Dennis Handly]

>Steven: it's in math. ">=" and ">" are different.

Or more particularly, edge arithmetic.