Re: [Xen-users] Xen LVM reducing HVM MS Windows guest disk

[StÃphane GAUDICHE <stephane.gaudiche@xxxxxxxxxxx>]

 > Message du 05/02/13 13:47
> De : "Ian Campbell" 
> A : "Stéphane GAUDICHE" 
> Copie à : "xen-users@xxxxxxxxxxxxx" 
> Objet : Re: [Xen-users] Xen LVM reducing HVM MS Windows guest disk
>
> On Thu, 2013-01-31 at 17:36 +0000, Stéphane GAUDICHE wrote:
> > Hello list,
> > 
> > I run xen 4.0 on a debian squeeze host with local lvm2 storage
> > I've got HVM VMs (Microsoft Windows) with 2 drives (c: [OS] & D:
> > [Data]), file system: NTFS
> > I want to reduce the size of the D: drive of my HVMs.
> > 
> > By reading several articles and howtos across web,
> > 1- I backup datas first outside the XenHost
> > 2- then from MSWindows guest-OS, I managed to live-reduce the
> > partition's size on the D: drive (from 150G to 50G) with the embedded
> > tool "diskpart": "shrink" operator, it worked just fine.
> > 3- I power off the HVM.
> > Now, from xen point of view, i got a Logical Volume called
> > data_HVM_microsoft.img of (steal) 150G.
> > 4- I was expecting to do an "lvreduce" to reduce the logical volume
> > (the box) to 100G only
> 
> Why 100GB if you are reducing to 50GB?

Just to be large! ;) in case of...

> 
> > but what happen to the filesystem (contenant in the box),which is seen
> > as a D: drive from the HVM with a small 50G NTFS partition from now)
> > Do I care about it?
> 
> If you have reduced the filesystem within the guest to 50GB then only
> the first 50GB of the device will be used, so you should be able to
> safely reduce the LV.
 
 "the first 50GB" is a good news
 "you should be able to safely reduce" doesn't sound very good for me.
 
 > You'd want to be damned sure that you had indeed
> reduced the filesystem to 50GB and not e.g. 50.1GB though, or else you
> will end up truncating it.

 That's why I make it larger than less.
 
> Note that resizing the filesystem in the guest will have no impact on
> the size of the underlying virtual device, nor will it affect the size
> of the LVM volume backing the device. I'm not sure if you were expecting
> that it would.

 Quite evidente for me, non-sense if not.
 
> > I note that the logical volume were seen as Block-device from xen host
> > file-system (not sure, but i guess it quite nomal due to LVM).
> > then
> > 5-check lv
> > 6-power on HVM
> > 7-extend D: drive to 100G
> 
> Why reduce to 50GB and then increase to 100GB?

Just to be large! ;) in case of...

> 
> > Can anyone help to understand if am I right by following these step?
> 
> Well, they sound OK to me from a Xen POV. I'm not so familiar with the
> Windows side of things.
> 
> Perhaps you can experiment by taking an LVM snapshot of the device,
> which would avoid the risk of trashing the device until you know what
> the right procedure is.
> 
 > Ian.
> 
>
 
 I think it's a part of my problem Linux people don't deal with Windows  trouble, no mix happen cause it is no such transparent in W case. :(
 --
 Stéphane

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