cloudstack-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Darren Shepherd <>
Subject Re: [DISCUSS] Pluggable VM snapshot related operations?
Date Tue, 08 Oct 2013 20:57:55 GMT
Who is going to decide whether the hypervisor snapshot should actually
happen or not? Or how?


On Tue, Oct 8, 2013 at 12:38 PM, SuichII, Christopher
<> wrote:
> --
> Chris Suich
> NetApp Software Engineer
> Data Center Platforms – Cloud Solutions
> Citrix, Cisco & Red Hat
> On Oct 8, 2013, at 2:24 PM, Darren Shepherd <> wrote:
>> So in the implementation, when we say "quiesce" is that actually being
>> implemented as a VM snapshot (memory and disk).  And then when you say
>> "unquiesce" you are talking about deleting the VM snapshot?
> If the VM snapshot is not going to the hypervisor, then yes, it will actually be a hypervisor
snapshot. Just to be clear, the unquiesce is not quite a delete - it is a collapse of the
VM snapshot and the active VM back into one file.
>> In NetApp, what are you snapshotting?  The whole netapp volume (I
>> don't know the correct term), a file on NFS, an iscsi volume?  I don't
>> know a whole heck of a lot about the netapp snapshot capabilities.
> Essentially we are using internal APIs to create file level backups - don't worry too
much about the terminology.
>> I know storage solutions can snapshot better and faster than
>> hypervisors can with COW files.  I've personally just been always
>> perplexed on whats the best way to implement it.  For storage
>> solutions that are block based, its really easy to have the storage
>> doing the snapshot.  For shared file systems, like NFS, its seems way
>> more complicated as you don't want to snapshot the entire filesystem
>> in order to snapshot one file.
> With filesystems like NFS, things are certainly more complicated, but that is taken care
of by our controller's operating system, Data ONTAP, and we simply use APIs to communicate
with it.
>> Darren
>> On Tue, Oct 8, 2013 at 11:10 AM, SuichII, Christopher
>> <> wrote:
>>> I can comment on the second half.
>>> Through storage operations, storage providers can create backups much faster
than hypervisors and over time, their snapshots are more efficient than the snapshot chains
that hypervisors create. It is true that a VM snapshot taken at the storage level is slightly
different as it would be psuedo-quiesced, not have it's memory snapshotted. This is accomplished
through hypervisor snapshots:
>>> 1) VM snapshot request (lets say VM 'A'
>>> 2) Create hypervisor snapshot (optional)
>>>  -VM 'A' is snapshotted, creating active VM 'A*'
>>>  -All disk traffic now goes to VM 'A*' and A is a snapshot of 'A*'
>>> 3) Storage driver(s) take snapshots of each volume
>>> 4) Undo hypervisor snapshot (optional)
>>>  -VM snapshot 'A' is rolled back into VM 'A*' so the hypervisor snapshot no longer
>>> Now, a couple notes:
>>> -The reason this is optional is that not all users necessarily care about the
memory or disk consistency of their VMs and would prefer faster snapshots to consistency.
>>> -Preemptively, yes, we are actually taking hypervisor snapshots which means there
isn't actually a performance of taking storage snapshots when quiescing the VM. However, the
performance gain will come both during restoring the VM and during normal operations as described
>>> Although you can think of it as a poor man's VM snapshot, I would think of it
more as a consistent multi-volume snapshot. Again, the difference being that this snapshot
was not truly quiesced like a hypervisor snapshot would be.
>>> --
>>> Chris Suich
>>> NetApp Software Engineer
>>> Data Center Platforms – Cloud Solutions
>>> Citrix, Cisco & Red Hat
>>> On Oct 8, 2013, at 1:47 PM, Darren Shepherd <>
>>>> My only comment is that having the return type as boolean and using to
>>>> that indicate quiesce behaviour seems obscure and will probably lead
>>>> to a problem later.  Your basically saying the result of the
>>>> takeVMSnapshot will only ever need to communicate back whether
>>>> unquiesce needs to happen.  Maybe some result object would be more
>>>> extensible.
>>>> Actually, I think I have more comments.  This seems a bit odd to me.
>>>> Why would a storage driver in ACS implement a VM snapshot
>>>> functionality?  VM snapshot is a really a hypervisor orchestrated
>>>> operation.  So it seems like were trying to implement a poor mans VM
>>>> snapshot.  Maybe if I understood what NetApp was trying to do it would
>>>> make more sense, but its all odd.  To do a proper VM snapshot you need
>>>> to snapshot memory and disk at the exact same time.  How are we going
>>>> to do that if ACS is orchestrating the VM snapshot and delegating to
>>>> storage providers.  Its not like you are going to pause the VM.... or
>>>> are you?
>>>> Darren
>>>> On Mon, Oct 7, 2013 at 11:59 AM, Edison Su <> wrote:
>>>>> I created a design document page at,
feel free to add items on it.
>>>>> And a new branch "pluggable_vm_snapshot" is created.
>>>>>> -----Original Message-----
>>>>>> From: SuichII, Christopher []
>>>>>> Sent: Monday, October 07, 2013 10:02 AM
>>>>>> To: <>
>>>>>> Subject: Re: [DISCUSS] Pluggable VM snapshot related operations?
>>>>>> I'm a fan of option 2 - this gives us the most flexibility (as you
stated). The
>>>>>> option is given to completely override the way VM snapshots work
>>>>>> storage providers are given to opportunity to work within the default
>>>>>> snapshot workflow.
>>>>>> I believe this option should satisfy your concern, Mike. The snapshot
>>>>>> quiesce strategy would be in charge of communicating with the hypervisor.
>>>>>> Storage providers should be able to leverage the default strategies
>>>>>> simply perform the storage operations.
>>>>>> I don't think it should be much of an issue that new method to the
>>>>>> driver interface may not apply to everyone. In fact, that is already
the case.
>>>>>> Some methods such as un/maintain(), attachToXXX() and takeSnapshot()
>>>>>> already not implemented by every driver - they just return false
when asked
>>>>>> if they can handle the operation.
>>>>>> --
>>>>>> Chris Suich
>>>>>> NetApp Software Engineer
>>>>>> Data Center Platforms - Cloud Solutions
>>>>>> Citrix, Cisco & Red Hat
>>>>>> On Oct 5, 2013, at 12:11 AM, Mike Tutkowski <>
>>>>>> wrote:
>>>>>>> Well, my first thought on this is that the storage driver should
>>>>>>> be telling the hypervisor to do anything. It should be responsible
>>>>>>> creating/deleting volumes, snapshots, etc. on its storage system
>>>>>>> On Fri, Oct 4, 2013 at 5:57 PM, Edison Su <>
>>>>>>>> In 4.2, we added VM snapshot for Vmware/Xenserver. The current
>>>>>>>> workflow will be like the following:
>>>>>>>> createVMSnapshot api -> VMSnapshotManagerImpl: creatVMSnapshot
>>>>>>>> send CreateVMSnapshotCommand to hypervisor to create vm snapshot.
>>>>>>>> If anybody wants to change the workflow, then need to either
>>>>>>>> VMSnapshotManagerImpl directly or subclass VMSnapshotManagerImpl.
>>>>>>>> Both are not the ideal choice, as VMSnapshotManagerImpl should
>>>>>>>> able to handle different ways to take vm snapshot, instead
of hard code.
>>>>>>>> The requirements for the pluggable VM snapshot coming from:
>>>>>>>> Storage vendor may have their optimization, such as NetApp.
>>>>>>>> VM snapshot can be implemented in a totally different way(For
>>>>>>>> example, I could just send a command to guest VM, to tell
>>>>>>>> application to flush disk and hold disk write, then come
to hypervisor to
>>>>>> take a volume snapshot).
>>>>>>>> If we agree on enable pluggable VM snapshot, then we can
move on
>>>>>>>> discuss how to implement it.
>>>>>>>> The possible options:
>>>>>>>> 1. coarse grained interface. Add a VMSnapshotStrategy interface,
>>>>>>>> which has the following interfaces:
>>>>>>>>  VMSnapshot takeVMSnapshot(VMSnapshot vmSnapshot);
>>>>>>>>  Boolean revertVMSnapshot(VMSnapshot vmSnapshot);
>>>>>>>>  Boolean DeleteVMSnapshot(VMSnapshot vmSnapshot);
>>>>>>>> The work flow will be: createVMSnapshot api ->
>>>>>> VMSnapshotManagerImpl:
>>>>>>>> creatVMSnapshot -> VMSnapshotStrategy: takeVMSnapshot
>>>>>>>> VMSnapshotManagerImpl will manage VM state, do the sanity
>>>>>>>> then will handle over to VMSnapshotStrategy.
>>>>>>>> In VMSnapshotStrategy implementation, it may just send a
>>>>>>>> Create/revert/delete VMSnapshotCommand to hypervisor host,
or do
>>>>>>>> anything special operations.
>>>>>>>> 2. fine-grained interface. Not only add a VMSnapshotStrategy
>>>>>>>> interface, but also add certain methods on the storage driver.
>>>>>>>>  The VMSnapshotStrategy interface will be the same as option
>>>>>>>>  Will add the following methods on storage driver:
>>>>>>>> /* volumesBelongToVM  is the list of volumes of the VM that
>>>>>>>> on this storage, storage vendor can either take one snapshot
for this
>>>>>>>> volumes in one shot, or take snapshot for each volume separately
>>>>>>>>     The pre-condition: vm is unquiesced.
>>>>>>>>     It will return a Boolean to indicate, do need unquiesce
vm or not.
>>>>>>>>     In the default storage driver, it will return false.
>>>>>>>>  */
>>>>>>>>  boolean takeVMSnapshot(List<VolumeInfo> volumesBelongToVM,
>>>>>>>> VMSnapshot vmSnapshot);
>>>>>>>>  Boolean revertVMSnapshot(List<VolumeInfo> volumesBelongToVM,
>>>>>>>> VMSnapshot vmSnapshot);
>>>>>>>> Boolean deleteVMSnapshot(List<VolumeInfo> volumesBelongToVM,
>>>>>>>> VMSnapshot vmSNapshot);
>>>>>>>> The work flow will be: createVMSnapshot api ->
>>>>>> VMSnapshotManagerImpl:
>>>>>>>> creatVMSnapshot -> VMSnapshotStrategy: takeVMSnapshot
-> storage
>>>>>>>> driver:takeVMSnapshot In the implementation of VMSnapshotStrategy's
>>>>>>>> takeVMSnapshot, the pseudo code looks like:
>>>>>>>>     HypervisorHelper.quiesceVM(vm);
>>>>>>>>     val volumes = vm.getVolumes();
>>>>>>>>     val maps = new Map[driver, list[VolumeInfo]]();
>>>>>>>>     Volumes.foreach(volume => maps.put(volume.getDriver,
volume ::
>>>>>>>> maps.get(volume.getdriver())))
>>>>>>>>     val needUnquiesce = true;
>>>>>>>>      maps.foreach((driver, volumes) => needUnquiesce 
>>>>>>>> needUnquiesce && driver.takeVMSnapshot(volumes))
>>>>>>>>    if (needUnquiesce ) {
>>>>>>>>     HypervisorHelper.unquiesce(vm);
>>>>>>>>  }
>>>>>>>> By default, the quiesceVM in HypervisorHelper will actually
take vm
>>>>>>>> snapshot through hypervisor.
>>>>>>>> Does above logic makes senesce?
>>>>>>>> The pros of option 1 is that: it's simple, no need to change
>>>>>>>> driver interfaces. The cons is that each storage vendor need
>>>>>>>> implement a strategy, maybe they will do the same thing.
>>>>>>>> The pros of option 2 is that, storage driver won't need to
>>>>>>>> about how to quiesce/unquiesce vm. The cons is that, it will
>>>>>>>> these methods on each storage drivers, so it assumes that
this work
>>>>>>>> flow will work for everybody.
>>>>>>>> So which option we should take? Or if you have other options,
>>>>>>>> let's know.
>>>>>>> --
>>>>>>> *Mike Tutkowski*
>>>>>>> *Senior CloudStack Developer, SolidFire Inc.*
>>>>>>> e:
>>>>>>> o: 303.746.7302
>>>>>>> Advancing the way the world uses the
>>>>>>> cloud<>
>>>>>>> *(tm)*

View raw message