[linux-lvm] Is my xen hosting tech support misleading me?

[linux-lvm] Is my xen hosting tech support misleading me?

[Shachar Or]

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Hello.

Attached is a question I've asked my xen hosting provider's technical
support and the answer they've supplied.

Sam sais "There is no LVM module available, so you would need to compile
LVM by yourself from the Xen kernel sources." but I've no problem
loading dm_mod and to my understanding of LVM, this is the only module
needed. So is he just wrong?

Thanks.

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Hello, 

Thank you for your patience.

There is no LVM module available, so you would need to compile LVM by yourself from the Xen kernel sources.

You will then need to activate the module.

You should be able to find the appropriate help online.


I am at your disposal should you need any further information.

Best regards,
Sam

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Product     : hosting
Category    : 
Question    : 
FirstName   : Shachar
LastName    : Or
CompanyName : 
Email       : dawnlight@lavabit.com
Domain      : 
DomainNB    : 
Handle      : SO866-GANDI
Anciennet  : 
Transaction : 
Message     : Hello.

This is a technical question about a problem I'm experiencing with LVM on my virtual server.

The issue is that logical volumes are not activated on bootup. This prevents me from using /etc/fstab to mount them.

root@shacharor:~# lvdisplay | grep 'LV Status' && udevtrigger && udevsettle && lvdisplay | grep 'LV Status'
  LV Status              NOT available
  LV Status              available
root@shacharor:~#

This shows that udev handles logical volumes correctly and does activate them. But why doesn't it do it on bootup?

Thanks.



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Re: [linux-lvm] Is my xen hosting tech support misleading me?

[Tim Post]

On Tue, 2009-02-03 at 09:02 +0200, Shachar Or wrote:
> Hello.
> 
> Attached is a question I've asked my xen hosting provider's technical
> support and the answer they've supplied.
> 
> Sam sais "There is no LVM module available, so you would need to compile
> LVM by yourself from the Xen kernel sources." but I've no problem
> loading dm_mod and to my understanding of LVM, this is the only module
> needed. So is he just wrong?

Probably, however your going to need to find out if you have the entire
dm_* family for the functionality that you want (i.e. snapshots). You
should (on your VM) simply be able to install lvm2 via yum, apt-get or
whatever packaging mechanism is provided by your distribution.

I use lvm2 on literally hundreds of paravirtualized Xen guests without a
problem.

A word of warning, don't make LV's (or their snapshots) a prerequisite
to boot .. since you have no control over your initrd. If your provider
has given you xvda and xvdb , use xvdb for your pv, keep the root file
system on xvda. 

Cheers,
--Tim


> 
> Thanks.
> email message attachment, "הודעה מועברת - <Ref1876314> DOMAIN :"
> > -------- Forwarded Message --------
> > From: Gandi Hosting <hosting@support.gandi.net>
> > To: dawnlight@lavabit.com
> > Subject: <Ref1876314> DOMAIN :
> > Date: Mon, 2 Feb 2009 15:09:28 +0100 (CET)
> > 
> > Hello, 
> > 
> > Thank you for your patience.
> > 
> > There is no LVM module available, so you would need to compile LVM
> > by yourself from the Xen kernel sources. 
> > 
> > You will then need to activate the module. 
> > 
> > You should be able to find the appropriate help online.
> > 
> > 
> > I am at your disposal should you need any further information.
> > 
> > Best regards,
> > Sam
> > 
> > ---------------------------------------
> > Are you satisfied with the quality of the reply you received?
> > YES: http://www.gandi.net/faq/feedback/yes
> > NO: http://www.gandi.net/faq/feedback/no
> > 
> > I would like to give more detailed feedback:
> > http://www.gandi.net/faq/feedback
> > ---------------------------------------
> > 
> > 
> > 
> > Help about hosting / aide sur l'hébergement: http://wiki.gandi.net/
> > 
> > GANDI
> > http://www.gandi.net 
> > 
> > 
> > -------------------------------------- 
> > Product     : hosting 
> > Category    :  
> > Question    :  
> > FirstName   : Shachar 
> > LastName    : Or 
> > CompanyName :  
> > Email       : dawnlight@lavabit.com 
> > Domain      :  
> > DomainNB    :  
> > Handle      : SO866-GANDI 
> > Anciennet  :  
> > Transaction :  
> > Message     : Hello. 
> > 
> > This is a technical question about a problem I'm experiencing with LVM on my virtual server. 
> > 
> > The issue is that logical volumes are not activated on bootup. This prevents me from using /etc/fstab to mount them. 
> > 
> > root@shacharor:~# lvdisplay | grep 'LV Status' && udevtrigger && udevsettle && lvdisplay | grep 'LV Status' 
> >   LV Status              NOT available 
> >   LV Status              available 
> > root@shacharor:~# 
> > 
> > This shows that udev handles logical volumes correctly and does activate them. But why doesn't it do it on bootup? 
> > 
> > Thanks. 
> > 
> > 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Is my xen hosting tech support misleading me?

[Tim Post]

Sorry to top post, but of course make sure the appropriate modules are
loaded on boot (again, emphasis on not needing them to pivot_root)
unless you have a VERY cooperative provider.

Cheers,
--Tim

On Tue, 2009-02-03 at 15:34 +0800, Tim Post wrote:
> On Tue, 2009-02-03 at 09:02 +0200, Shachar Or wrote:
> > Hello.
> > 
> > Attached is a question I've asked my xen hosting provider's technical
> > support and the answer they've supplied.
> > 
> > Sam sais "There is no LVM module available, so you would need to compile
> > LVM by yourself from the Xen kernel sources." but I've no problem
> > loading dm_mod and to my understanding of LVM, this is the only module
> > needed. So is he just wrong?
> 
> Probably, however your going to need to find out if you have the entire
> dm_* family for the functionality that you want (i.e. snapshots). You
> should (on your VM) simply be able to install lvm2 via yum, apt-get or
> whatever packaging mechanism is provided by your distribution.
> 
> I use lvm2 on literally hundreds of paravirtualized Xen guests without a
> problem.
> 
> A word of warning, don't make LV's (or their snapshots) a prerequisite
> to boot .. since you have no control over your initrd. If your provider
> has given you xvda and xvdb , use xvdb for your pv, keep the root file
> system on xvda. 
> 
> Cheers,
> --Tim
> 
> 
> > 
> > Thanks.
> > email message attachment, "הודעה מועברת - <Ref1876314> DOMAIN :"
> > > -------- Forwarded Message --------
> > > From: Gandi Hosting <hosting@support.gandi.net>
> > > To: dawnlight@lavabit.com
> > > Subject: <Ref1876314> DOMAIN :
> > > Date: Mon, 2 Feb 2009 15:09:28 +0100 (CET)
> > > 
> > > Hello, 
> > > 
> > > Thank you for your patience.
> > > 
> > > There is no LVM module available, so you would need to compile LVM
> > > by yourself from the Xen kernel sources. 
> > > 
> > > You will then need to activate the module. 
> > > 
> > > You should be able to find the appropriate help online.
> > > 
> > > 
> > > I am at your disposal should you need any further information.
> > > 
> > > Best regards,
> > > Sam
> > > 
> > > ---------------------------------------
> > > Are you satisfied with the quality of the reply you received?
> > > YES: http://www.gandi.net/faq/feedback/yes
> > > NO: http://www.gandi.net/faq/feedback/no
> > > 
> > > I would like to give more detailed feedback:
> > > http://www.gandi.net/faq/feedback
> > > ---------------------------------------
> > > 
> > > 
> > > 
> > > Help about hosting / aide sur l'hébergement: http://wiki.gandi.net/
> > > 
> > > GANDI
> > > http://www.gandi.net 
> > > 
> > > 
> > > -------------------------------------- 
> > > Product     : hosting 
> > > Category    :  
> > > Question    :  
> > > FirstName   : Shachar 
> > > LastName    : Or 
> > > CompanyName :  
> > > Email       : dawnlight@lavabit.com 
> > > Domain      :  
> > > DomainNB    :  
> > > Handle      : SO866-GANDI 
> > > Anciennet  :  
> > > Transaction :  
> > > Message     : Hello. 
> > > 
> > > This is a technical question about a problem I'm experiencing with LVM on my virtual server. 
> > > 
> > > The issue is that logical volumes are not activated on bootup. This prevents me from using /etc/fstab to mount them. 
> > > 
> > > root@shacharor:~# lvdisplay | grep 'LV Status' && udevtrigger && udevsettle && lvdisplay | grep 'LV Status' 
> > >   LV Status              NOT available 
> > >   LV Status              available 
> > > root@shacharor:~# 
> > > 
> > > This shows that udev handles logical volumes correctly and does activate them. But why doesn't it do it on bootup? 
> > > 
> > > Thanks. 
> > > 
> > > 
> > _______________________________________________
> > linux-lvm mailing list
> > linux-lvm@redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-lvm
> > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
> 
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

Re: [linux-lvm] Is my xen hosting tech support misleading me?

[David Robinson]

> Attached is a question I've asked my xen hosting provider's technical
> support and the answer they've supplied.
>
> Sam sais "There is no LVM module available, so you would need to compile
> LVM by yourself from the Xen kernel sources." but I've no problem
> loading dm_mod and to my understanding of LVM, this is the only module
> needed. So is he just wrong?

If you're able to activate the volumes after the system has booted
(which the discussion below suggests), then the device-mapper modules
would already be available so there's no need to compile anything.

> The issue is that logical volumes are not activated on bootup. This prevents me from using /etc/fstab to mount them.
>
> root@shacharor:~# lvdisplay | grep 'LV Status' && udevtrigger && udevsettle && lvdisplay | grep 'LV Status'
>   LV Status              NOT available
>   LV Status              available
> root@shacharor:~#
>
> This shows that udev handles logical volumes correctly and does activate them. But why doesn't it do it on bootup?

If the volumes aren't created at boot time you're probably missing the
relevant stuff in your initial ram disk... usually, if you're root fs
is on an LVM volume, the ram disk would contain the relevant dm_*
kernel modules and a script that (amongst other things) loads the
relevant kernel modules and activates the volumes. Your simplest
solution may be to just add "vgscan --mknodes" and "vgchange -ay" to
rc.local (its uglier than fixing the initrd, but you may not be able
to recreate the initrd in your situation).

--Dave