Virtualization: Storage Live Migration
Why do we need Storage Live Migration?
VMware Storage VMotion has set the standard for storage live migration, and we need to support this feature both in RHEL/KVM and RHEV. It is not just a checkbox, but a major feature that KVM needs to support. Storage Live Migration will be used in data-center virtualization, significantly enhancing capital and operational efficiency.
How does it work?
Storage Live Migration enables live migration of virtual machine disk files across storage disks and arrays. This feature allows a customer to relocate virtual machine disk files between and across shared storage locations while maintaining continuous service availability and data integrity. The live block copy feature allows an image backing a
guest disk to be copied while the guest is online. The streaming feature allows the guest to start execution while the parent image reside remotely (with/without shared storage).
Where is it supported?
The Storage Live Migration feature will be supported in RHEL/KVM, and libvirt will provide the necessary feature set for competing with VMware Storage VMotion. Storage Live Migration will be used by Red Hat virtualization customers as part of an end-to-end virtualization solution that is designed to enable pervasive data-center virtualization.
Please comment how important this feature is for you, for your use case.
Responses
Guru
6222 points
Hello Bhavna Sarathy,
Without this feature I do not see VMware being replaced in many datacenters.
So I guess it is a very important feature.
Kind regards,
Jan Gerrit Kootstra
Guru
3262 points
I work with a several thousand VM virtualization environment and Storage Live Migration is absolutely a useful feature--it is a key product differentiator (KPD) at the moment and KVM adopting the feature would be a big win.
Red Hat
Active Contributor
360 points
Phil, thanks for response, and it would be great to hear some details regarding your environment. Would you mind sharing some details? I want to be sure we architect and implement to match your use case, and others out there. We should be targetting the big data centers.
Regards,
Bhavna
Guru
3262 points
Hi Bhavna,
We use VMware predominantly at the moment, supporting clusters of MTAs, archiving servers and mail stores. We rely mostly on local storage, but use Storage vMotion as necessary when we need to migrate data from one host to another. Our primary use case would be on-demand migration of virtual machines to support balancing workloads.
Phil
As we try to push RHEV to customers, storage live migration is one of the most asked question nowadays (It was P2V before, but not anymore - thanks to Acronis). We approached a big GLC in my country and as much as they like RHEV (we are in the POC stage right now), the features that get ask the most is Storage Live Migration. Although most customers dont use it in VMware environment (at least in my customer demographic), this GLC is a big user of Storage VMotion from VMware.
This feature sometime is a make or break for some big customers. And in order for RHEV to penetrate to major accounts and replacing VMware as a serious alternatives, this must come in ASAP.
Without good storage management features like Storage vmotion RHEV has a big challenge competing VMware, so it's a +1 from me. As for use case, well, that's kind of obvious. If you have vm's living on different datastores the need to move them between datastores automatically arises. Within an enterprise environment an obvious consequence of this is that we want to do this without shutting down the vm.
I do agree with with the Storage Live Migration feature stated above. It should be a must.
I would also like to share some comments by one of our customers during a PoC of RHEV:
- Inability to use an existing virtual disk to another guest
- Need to shutdown guests in order to take snapshots
- Inability to extend the size of a virtual disk
- Inability to increase the size of a Data Storage
- The way “snapcloning” is done requires double the disk space required
- Inability to use Physical SAN disks on a guest
I believe the above features should also be considered.
The points made in this post are the same things that we get asked when we discuss RHEV with other agencies. They all use VMWare, and they consider RHEV to not be fully Enterprise ready without the majority of the features listed here. Granted, RHEV is a younger product, but some resources should be devoted to knocking out at least two of these points for the near feature.
Red Hat
Active Contributor
360 points
Thanks for all the feedback on this thread. Having to shutdown guests to take a snapshot is not seen kindly by customers. Live snapshots will be supported by the end of this year. Storage live migration is an important feature we are trying to implement in KVM soon. Definitely based on the feedback from this group, it's clear that we need to push this feature out in our Virtualization portfolio ASAP.
As far as I know this is now marginally possible in KVM via qemu-kvm 0.12 and higher. This feature looks to be in active development for KVM.
http://www.linux-kvm.com/content/qemu-kvm-012-adds-block-migration-feature
I'd love to see this and have an API available so great file systems like zfs (the ZfsOnLinux (ZOL) team is FANTASTIC) and brtfs, etc could use snapshot migration to make the process really smooth.
I'd like the same kind of API available for the new vss snapshot feature so zfs can use it's snapshots for that, the ZOL team has clearly communicated to me they would look at implementing it.
http://www.google.com/url?sa=t&rct=j&q=kvm%20snapshot%20vss&source=web&cd=1&ved=0CDQQFjAA&url=https%3A%2F%2Fevents.linuxfoundation.org%2Fslides%2F2011%2Flinuxcon-japan%2Flcj2011_sorensen.pdf&ei=CqzSUN-7CYjDrQGV04HADg&usg=AFQjCNHgvX5gUmO2kXaSEJYn-Jmu_zD2CA&bvm=bv.1355534169,d.aWM&cad=rja
We've moved from Hyper-V to KVM (dispite 2012 now supporting live migration, but we also have ZFS under ALL our data so moving from system A to be right now only takes the time for 1 reboot. It's be great to make that 0 down time :).
BK
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