[linux-lvm] when to vgscan/pvscan/lvscan

[linux-lvm] when to vgscan/pvscan/lvscan

[Philippe Cerfon]

(seems that this did not came through the first time?!)

Hi.

(Talking always about lvm2...)

Is there a real technical difference between pvscan, vgscan and lvscan?
I mean as far as I understand one always needs all information about
PVs,VGs and LVs in order to get the later.
So apart from different textual "debug" output, do all the same, i.e.
scanning over all configured block devices, looking for PVs and
scanning their VG-descriptors in order to get the information about al
LVs?


Is there ever the need to rund pvscan/vgscan/lvscan manually and if so
in which cases? I mean the vgscan manpage says that this happens
automatically in lvm2, so if I e.g. have my init-scripts and want to
make the LVs available, is it generally enough to do
vgchange -an
or can there be cases when the preceding vgscan is still required?


Thanks,
Philippe.

[linux-lvm] when to vgscan/pvscan/lvscan

[Philippe Cerfon]

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Hi.

(Talking always about lvm2...)

Is there a real technical difference between pvscan, vgscan and lvscan?
I mean as far as I understand one always needs all information about
PVs,VGs and LVs in order to get the later.
So apart from different textual "debug" output, do all the same, i.e.
scanning over all configured block devices, looking for PVs and
scanning their VG-descriptors in order to get the information about al
LVs?


Is there ever the need to rund pvscan/vgscan/lvscan manually and if so
in which cases? I mean the vgscan manpage says that this happens
automatically in lvm2, so if I e.g. have my init-scripts and want to
make the LVs available, is it generally enough to do
vgchange -an
or can there be cases when the preceding vgscan is still required?


Thanks,
Philippe.


      

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Re: [linux-lvm] when to vgscan/pvscan/lvscan

[Alasdair G Kergon]

The code is supposed to auto-detect changes, but there are still
(mostly obscure) ways that confuse it.

The safest approach if you want to remove the vgscan at boot is to
specify the precise VGs you want to activate by name on the vgchange
command line instead of letting it default to 'all'.

So 'vgchange -ay root_vg home_vg' etc. instead of 'vgchange -ay'.

Then it knows what VGs are supposed to be there, and if it didn't think
it needed to scan but doesn't see one or more of them that'll be enough
to trigger the scan.

Alasdair

Re: [linux-lvm] when to vgscan/pvscan/lvscan

[Philippe Cerfon]

Hi.
Thanks for your reply.

--- On Wed, 6/30/10, Alasdair G Kergon <agk@redhat.com> wrote:
>The safest approach if you want to remove the vgscan at boot is
>to specify the precise VGs you want to activate by name on the
>vgchange command line instead of letting it default to 'all'.
Is it also possible to scan for a specific LV?

When I use udev, will newly added devices be automatically scanned for LVM stuff (i.e. PVs) if they're block devices?

>Then it knows what VGs are supposed to be there, and if it didn't
>think it needed to scan but doesn't see one or more of them that'll
>be enough to trigger the scan.
Nice.

Thanks,
Philippe.