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From Donal Lafferty <donal.laffe...@citrix.com>
Subject RE: diskless boot
Date Tue, 19 Mar 2013 09:28:35 GMT


> -----Original Message-----
> From: Bjoern Teipel [mailto:bjoern.teipel@internetbrands.com]
> Sent: 19 March 2013 3:50 AM
> To: cloudstack-users@incubator.apache.org
> Subject: Re: diskless boot
> 
> On 3/18/2013 8:43 AM, Donal Lafferty wrote:
> > AFAIK, data disks are by default created in Primary Storage and not on
> > the hypervisor itself.  I take it you want the replacement server for
> > a VM to sit in a different cluster that does not have access to the
> > same primary storage
> >
> > Did you mean to ask whether the data disk is a 'dyanmic' hard drive image?
> > 'Dynamic' disks are about as large as the actual data stored on it.  They do not
> > reserve spaced in the store for portions of the disk that have no data.  In this
> > case, I do not know the answer, as I've not much experience with KVM.
> No I was more talking about the thin provisioning at LVM because I was
> considering to boot those disk less VMs with the 1GB data disk on hyper visor
> with local storage not to waste precious NAS.
> That's why I was thinking of thin provisioning of LVM
[Donal Lafferty] 
Whether or not to use local storage is a separate issue from whether or not to use dynamic
disks.  There is an option for creating local storage data disks when you create a new disk
offering.  I would guess that this is a 'dynamic' hard drive image, and not a 'thin provisioned'
image.

> >
> > IIRC, 'thin' as in 'thin provisioning' relates to templates.  To reduce the foot
> > print of the root device, a read/write 'diff' disk is created and linked to a read
> > only 'base' disk.  The 'base' disk is a copy of the template image.  The diff
> > captures changes, and grows over time as the VM updates.  Because a
> > number of VMs use the same 'base' image, template transfer time and the
> > foot print of the root device is substantially reduced.
> That's the reason why we have patchdisk files ?
[Donal Lafferty] 
Patchdisk on KVM pass VM-specific data, whereas 'thin provisioning' is about reusing the same
base image across several VMs.

>From http://markmail.org/message/anaolzxlcpgrlnh5

"For those who don't know (this probably doesn't matter, but...), when KVM brings up a system
VM, it creates a 'patchdisk' on primary storage. This patchdisk is used to pass along 1) the
authorized_keys file and 2) a 'cmdline' file that describes to the systemvm startup services
all of the various properties of the system vm."

> >
> >
> > -----Original Message-----
> > From: Teipel, Bjoern [mailto:bjoern.teipel@internetbrands.com]
> > Sent: 18 March 2013 3:24 PM
> > To: cloudstack-users@incubator.apache.org
> > Cc: cloudstack-users@incubator.apache.org
> > Subject: Re: diskless boot
> >
> > Hi Donal,
> >
> > I didn't try thin provisioning on a local LVM disk but I would expect that is
> takes only few MB. Does CS support thin on local storage (LVM)?
> >
> > I can see where you question is going but a data disk,even empty would
> create a dependency to the hypervisor.
> > The idea for using disk less boot is not to create any dependency on
> storage and only rely on memory/CPU. If the hypervisor goes down I just
> start the VM in a new one.
> > A data disk would be here blocking and you have to remove the data disk
> from the VM before you can do any action on the VM. Doubt that would
> work in CS.
> >
> > Bjoern
> >
> > On Mar 18, 2013, at 4:00 AM, "Donal Lafferty" <donal.lafferty@citrix.com>
> wrote:
> >
> >> Let me rephrase that,
> >>
> >> Hi Bjoern,
> >>
> >> On the KVM deployment you are using, I take it that the 1 gig disk is a data
> disk.  It the problem that its unwieldy to manage or that 1 gig takes up too
> much room?
> >>
> >> Does the 1 gig data disk take up a lot of space on the primary storage?
> >>
> >> DL
> >>
> >>
> >>> -----Original Message-----
> >>> From: Mathias Mullins [mailto:mathias.mullins@citrix.com]
> >>> Sent: 18 March 2013 10:53 AM
> >>> To: cloudstack-users@incubator.apache.org
> >>> Subject: Re: diskless boot
> >>>
> >>> Thin or thick provisioned? On what type of file system?
> >>>
> >>> Thank you,
> >>> Matt
> >>>
> >>> On Mar 18, 2013, at 9:47 PM, "Donal Lafferty"
> >>> <donal.lafferty@citrix.com>
> >>> wrote:
> >>>
> >>>> Out of interest, how much space does an unused 1 Gig disk take up
> >>>> on a
> >>> hypervisor?
> >>>> DL
> >>>>
> >>>>> -----Original Message-----
> >>>>> From: Bjoern Teipel [mailto:bjoern.teipel@internetbrands.com]
> >>>>> Sent: 16 March 2013 6:12 AM
> >>>>> To: cloudstack-users@incubator.apache.org
> >>>>> Subject: diskless boot
> >>>>>
> >>>>> Hi guys,
> >>>>>
> >>>>> one of my questions is still open:
> >>>>>
> >>>>> - CS doesn't support booting over ISO only without attaching a disk.
> >>>>>    Background is, we migrate our datacenter to boot from ISO/PXE
and
> >>>>>    thats a big no go for me if I'm enforced to assign a 1G disk.
> >>>>>    Also set the minimum disk size to 0G in the global settings but
> >>>>>    I can't create "No Disk" Disk offerings ...
> >>>>>
> >>>>> Nobody had the desire to boot disk less other than me ?
> >>>>> Can't believe that ;-)
> >>>>>
> >>>>> Thanks,
> >>>>> Bjoern


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