Stepping out of a subway car is an entirely different matter when it's moving!

Mobility of virtual machines is a sticky wicket. As open systems infrastructure becomes increasingly virtualized, administrators and managers wish to use the technology to balance workload, ease migration, and provide better availability. Although technology is improving, actually moving virtual machines is not always a piece of cake. Let’s lay down a baseline of information so we may begin a discussion on the true nature of virtual machine mobility.

Mobility of What?

Let us consider first the question of what exactly is being moved. Systems administrators often focus on “the machine”, which encompasses the operating system and configured state of the virtual machine itself. But the true “mass” of the system is its stored data. Hypervisor vendors have come up with different techniques of moving these two essential elements, reflecting the unique characteristics of each.

• The virtual machine is an instance of an operating system along with its state and configuration. Mobility of virtual machines requires all of this to be preserved, along with any I/O channels. Live migration of virtual machine requires that any active network sessions be maintained, along with RAM content, registers and buffers, and so many other elements.
• The virtual machine image (commonly referred to as “storage”) is the static content addressed by a virtual machine. Typically a VMDK or similar virtual disc image, it must be accessible to the virtual machine at all times. Live migration of a virtual machine image is tricky, but perhaps not quite as complex as live migration of a running operating system.

VMware, Microsoft, and others recognize these 2 distinct elements to be migrated, and have come up with a variety of complementary technologies for each:

• vMotion is VMware’s virtual machine migration solution, and has continually evolved with each iteration of the hypervisor. DRS leverages vMotion to automate mobility. VMware has also created Storage vMotion and Storage DRS as complements to handle mobility of virtual machine images.
• Microsoft Hyper-V Live Migration is conceptually similar to vMotion, though newer and less full-featured. With Hyper-V 3.0, Microsoft will introduce Storage Live Migration as a complementary technology akin to Storage vMotion. Most other virtual machine managers also support some form of live migration, though live migration of storage is less common.

Mobility in What State?

One of the key benefits of virtual machine technology is the ability to “run anywhere” on dissimilar hardware. From the very beginning, hypervisors have provided the ability to create a universal virtual machine image that would run on a variety of supported platforms.

This leads to one of the key values of server virtualization in the data center: Disaster recovery. The ability to take a virtual machine image and system state and bring it online after a disaster is a true revolution for open systems IT. The benefits of the single usage of server virtualization technology easily justify the investment to many businesses.

But this sort of “cold” migration seems passé when compared to the live or “hot” migration possible with technologies like VMware vMotion. Live migration is much more difficult, since active client sessions must be preserved in activity must not be greatly interrupted.

This is the second great question that must be asked when considering virtual machine mobility: In what state will the virtual machine be moved? Will it be a cold, powered down image of the system? A suspended or paused operating system image? Or a full, running machine?

Mobility to Where?

Once we have decided whether we are discussing virtual machine migration or movement of storage resources, we must consider the scope of the movement. The ability to move a virtual machine from one member of the cluster to another has now become fairly common. But what about systems that are not related in a cluster? Or that are spread over great distances?

• The nice thing about clusters is that they share resources before and after a virtual machine is moved. It is practical to move the running virtual machine, its storage, or both independently and to expect that performance will not dramatically suffer as a result. The cluster can also preserve network connections, and even I/O state, without much impact on clients or other external elements.
• It is a bit more difficult to move systems within a data center, since one must maintain the I/O connections that might be interrupted. It is fairly trivial to configure an IP network and storage array to allow multiple machines to access the same iSCSI or NFS storage resources. It is a little more difficult to configure Fibre Channel (and, by extension, FCoE) SAN’s to handle this sort of dynamic movement, but it is not impossible. Although moving a running machine from one network port to another could cause client access to be interrupted, technologies like VXLAN allow these sessions to continue, and improved network switching technology should reduce performance impact.
• Moving the machine to a different data center is another matter entirely. Stretching a layer-2 Ethernet LAN or Fibre Channel SAN across a metro or greater distance, while possible, will always be problematic. IP routing is flexible, but it takes time for changes to propagate when live machines are moved. And it is difficult to keep storage in sync over long distances due to the amount of time it takes for information to transit. Again, all of these challenges are being addressed in various ways, but they’re still hard!

Stephen’s Stance

Moving cold virtual machine images from system to system, or even across great distances, is one of the main selling points of server virtualization. But it becomes much more difficult to manage movement of virtual machines that are still running, especially outside cluster or across WAN links. When talking about virtual machine mobility, it is important to consider what is being moved, the state it is in, and where it is going.

Note: This discussion is part of “Building Virtual Infrastructure”, my new seminar series with Truth in IT.

© sfoskett for Stephen Foskett, Pack Rat, 2012. | Virtual Machine Mobility: Of What, and to Where and in What State?
This post was categorized as Enterprise storage, Features, Gestalt IT, Virtual Storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.

For more information on earlier updates, see my articles:

• Storage Fixes in VMware ESX Server 3.5 Update 2
• Storage Changes in VMware ESX 3.5 Update 3
• Storage Changes in VMware ESX 3.5 Update 4
  
• Storage Changes in the VMware vSphere 4 Family

One first step is VMware’s whitepaper, “What’s New in VMware vSphere 5.0 – Storage“.

Licensing and Availability of Features

VMware has once again changed the licensing and pricing model, throwing the Internet into a tizzy:

• “Advanced” has been eliminated, moving up to “Enterprise”
• Pooled vRAM entitlements work across the entire vCenter environment
• New features like Policy-Driven Storage and Storage DRS (along with SIOC) are exclusive to “Enterprise Plus” licenses
• VAAI, PSP multipathing, and Storage vMotion are only found in “Enterprise”
• Thin Provisioning and VADP are available regardless of edition

VMware mucked with vSphere licensing again...

Major New vSphere 5 Storage Features

Storage DRS

Storage DRS is the world’s worst-kept secret, with everyone and his brother talking about it for over a year. Like the existing VM DRS capability, Storage DRS creates resource clusters and automatically moves VMs between them. Storage DRS uses utilization and performance metrics to make the call, and has three modes of operation. It sounds awesome, but it’s an Enterprise Plus-only feature.

Storage APIs – Storage Awareness (VASA)

There’s not much information presently, but a VAAI companion is introduced in vSphere 5: The vSphere Storage APIs for Storage Awareness (VASA) is a communication mechanism for vCenter to detect array capabilities like RAID Level, Thin Provisioning State, Replication State, etc. This will come in handy for all the other features in vSphere 5, especially policy-driven storage!

Policy-Driven Storage

Another new Enterprise Plus feature is Policy-Driven Storage. This allows storage tiers to be defined in vCenter based on SLA, performance, and other metrics which are used during provisioning, cloning, Storage vMotion, and Storage DRS. It leverages VASA for metrics and characterization and supports all arrays in the HCL, regardless of whether they’re NFS, iSCSI, or FC. It includes easy compliance status reporting in vCenter as well.

FCoE Software Initiator

Those of us “in the know” about storage expected VMware to add software FCoE support, so it’s no surprise that they did. This dramatically expands the potential FCoE footprint from just the few CNAs already supported in vSphere 4. It appears to be based on Intel’s OpenFCoE, since it shows up as “Intel Corporation FCoE Adapter” in the GUI!

vSphere Storage Appliance (VSA)

VMware enters the virtual storage appliance (VSA) market with their own offering, the vSphere Storage Appliance (also called VSA). Aimed primarily at the SMB market, it’s actually fairly clever, replicating storage between two or three nodes in a cluster for high availability and using NFS for access rather than iSCSI. And unlike the Celerra UBER that so many techies loved, the VMware VSA is ready for production use!

Existing Storage Features Enhanced in vSphere 5

VMFS 5

VMFS has been improved for scalability and efficiency, but the 2 TB limit on VMDKs remains (except for physical RDM). Only storage geeks like me need to worry about the specifics, but suffice to say that VMFS 5 requires less tuning and worrying and ought to scale and perform better thanks to increased maximums and leveraging the Atomic Test and Set (ATS) technology also used in VAAI. For newly-created volumes, there’s no more block size tuning, and alignment issues are addressed.

Storage APIs – Array Integration (VAAI 2)

See also VMware VAAI Storage Array Support in Plain English

VAAI has been revved, bringing back Thin Provisioning Stun (the AWOL “fourth primitive”) and adding NFS support.

There are now five block primitives for VAAI, depending on if you count thin space reclaim. This is really more of a bug fix than anything, since most folks assumed that the existing thin support already reclaimed deleted VMs and vMotioned VMDKs. I’m more interested in the addition of SCSI UNMAP in addition to WRITE_SAME! There’s also some additional T10 support, though I’m not clear on what it is or where it works.

We’ve also got VAAI for NFS environments now. NAS had sweet thin provisioning support even before block datastores, but the new Reserve Space command adds thick provisioning if that’s what you like. We’ve also got Full File Clone, which is like Full Copy for NFS but doesn’t work with Storage vMotion. And there’s some Extended Stats API to bring in more detail on file status. I also hear there’s an API for Native Snapshot Support, but it’s not widely discussed. Finally, note that NFS plugins come from vendors, not VMware as is the case for block VAAI.

Storage I/O Control

SIOC is enhanced for use in Storage DRS environments, becoming aware of the new datastore clusters. It also gets NFS support, and presumably uses VASA for metrics. But it’s still only available with Enterprise Plus licenses.

iSCSI Initiator GUI

The solid vSphere iSCSI initiator gets a friendly GUI for configuration. I like friendly iSCSI GUIs – just ask Microsoft!

Storage vMotion

The mechanism behind Storage vMotion has changed for a third time in as many releases, this time using “Mirror Mode” to mirror writes to in-progress vMotions. It also now supports migration of vSphere snapshots and Linked Clones. This can be offloaded for VAAI block, but not NFS.

vSphere Replication

New in vCenter Site Recovery Manager 5.0 is software-based replication. Although not technically a vSphere 5 feature, this is a major new storage feature in the VMware world. It allows any-to-any software-based storage replication for disaster recovery.

Stephen’s Stance

Once again, VMware added a ton of new storage enhancements to vSphere. With storage rapidly becoming the limiting factor in scalability and performance of virtual machine environments, this is no surprise. Also not surprising is the fact that major features like Policy-Driven Storage and Storage DRS (along with SIOC) are exclusive to “Enterprise Plus” licenses. I can’t blame VMware for making a buck, but it would be nice if more capabilities were available to the small shops!

I’ll be writing on all these features in detail shortly. Watch this space!

© sfoskett for Stephen Foskett, Pack Rat, 2011. | Storage Changes in VMware vSphere 5
This post was categorized as Enterprise storage, Features, Virtual Storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.

Great! But I thought the new era for IT was a cloud with choice, mobility, and application support, as trumpeted by EMC’s VMware subsidiary! Wasn’t Cloud vServices from VDC-OS supposed to be the prototype cloud strategy for the datacenter?

What we have here is a simple clash of marketing amusingly taking place at (nearly) the same company. VMware figured out how to extend their server virtualization products outside the confines of the data center, and laid that technology out as a strategy with the trendy “cloud” name. Meanwhile, mother EMC is working on next-generation content storage software and decides to roll that out as a strategy and also jumps on the “cloud” meme. What’s an IT manager to do?

Defining Atmos

As predicted, EMC’s Atmos (code-name Maui) is a distributed software layer to handle the storage and management of data objects across geographically-dispersed storage devices. EMC’s Chuck Hollis demonstrates Atmos with a simple, practical example, perhaps making it sound too much like Akamai but generally getting the point across. You have a data object, write it to Atmos through REST/SOAP or CIFS/NFS, assign some metadata, and the software takes care of data placement for you. It’ll add local copies, replicate for availability and performance, compress or deduplicate, manage versions, and all sorts of goodies (if you ask it to).

But EMC already has a capable object storage platform, the Centera. We’ve just got used to the content-addressable storage (CAS) label for object storage (even though this name misses the point of object storage, in my opinion) and now EMC wants us to learn a new label for a somewhat-similar device? Steve Todd, EMC’s object guy extraordinaire, lays it out:

SAN Value = Centralized, secure multi-tenancy for blocks.

NAS Value = Centralized, secure multi-tenancy for files.

CAS Value = Centralized, secure multi-tenancy for objects (content + metadata).

COS Value = Globalized, secure multi-tenancy for content with rich policies.

Ok, so the defining capabilities of Atmos are its global scale and rich policies. And the fact that “objects” has become “content”, presumably since Atmos can handle traditional NAS (CIFS/NFS) chores as well.

Prayers Answered?

It sounds like EMC is answering my prayers for a storage revolution, delivering a highly-capable object storage platform that transcends the old limits of blocks, directories, and files. Steve Todd points out that Atmos handles five policy categories out of the box:

• Replication
• Compression
• Spin-down
• Object de-dup
• Versioning

So we write some data to Atmos, using either traditional NAS or webby dubby protocols like SOAP, and can then apply policies in any of these five categories to that data. One can also extend the Atmos to accept other policies, but the absence (out of the box) of concepts like encryption, secure deletion, retention, and access control are surprising.

I am quite puzzled about how practical these policy capabilities will be in the real world. How exactly would an application say “I want you to compress that file I wrote over NFS just now?” Hitachi’s HCAP platform, for example, also has policy capabilities and a NAS front end, and although archiving applications can communicate their policy needs, I don’t see lots of current general-purpose applications using it.

Strategic Storage?

This brings me to my puzzlement: The default Atmos policies are all general-purpose, production computing ideas, not the special-purpose, archiving and retention needs served by Centera, HCAP, and the rest. So the Atmos is clearly intended to be a production data storage system, not an archiving system to compete with Centera.

Since mainstream business applications currently don’t have any capability to specify policies like these when writing files, and since NAS protocols lack any means to communicate them even if the apps want to, we can conclude that EMC expects that Atmos users will write special applications to take advantage of it.

EMC certainly doesn’t expect that the NAS-capable Atmos will simply replace today’s distributed NAS solutions. NAS is a sideshow for Atmos. The real action will be in the REST/SOAP webby dubby applications that will be written with the platform in mind and will take full advantage of these capabilities.

If this is true, and I and others suspect that it is, then Atmos really isn’t a game-changing platform unless you change your game. If you write new applications to store data with SOAP, Atmos is a nice in-house alternative to Amazon S3 or Nirvanix, and offers a very compelling set of data management capabilities. And if you want to set up shop to compete with those service providers, Atmos is a dream come true with built-in multi-tenancy.

Datacenter Strategy

So EMC alone has two seemingly competitive datacenter strategies. And then there’s Microsoft, which announced its Azure cloud platform recently, and Amazon and the other cloud providers.

So let’s say you’re a CIO for a large corporation. Which of the following strategies is more compelling:

1. Use VMware VDC-OS to add capabilities and Cloud vServices extend your current virtual infrastructure geographically
2. Recompile and tweak your Windows applications to leverage Microsoft Azure
3. Develop new applications to take advantage of the impressive storage capabilities of an in-house EMC Atmos system
4. Point your new applications at a third-party cloud provider like Amazon or Nirvanix

IT people are practical. Although we love new technology, we tend to be cautious. We also hate massive software development efforts, and only sanction them when they’re absolutely necessary. Given these personality traits, I’d say VDC-OS and perhaps Cloud vServices still stands out as the most likely and practical scenario for the majority of applications and businesses.

This is not to say that EMC Atmos will be a flop. I’m impressed by the technology, and expect that Atmos will find buyers, just as Centera did. And Atmos might even replace Centera once EMC adds retention policies to it and scales it down as well as up and out. But Atmos will not redefine the datacenter. We’re stuck with blocks and files, and VMware’s practical strategy is a winner in that world.

Update: Marc Farley compares Atmos to WAFS, with ominous implications, and echos my recent question on what is and is not innovative.

Update 2: Chuck Hollis, Storagezilla, and Len Devanna have all come right out and said that this is only intended for certain customers with massive distributed storage needs, and is not intended as a new datacenter strategy. Even the “cloudfella” says “ciao”:

Update 3: More great information, including a reply regarding VDC-OS and Atmos from the one and only Chad Sakac, more great detail about the inner workings of Atmos from Steve Todd, and even more info from Dave Graham. Finally, although I think that Cloudfellas video is cute, I wouldn’t categorize it as viral. But those Mozy ads are awesome!

See my posts on Gestalt IT for similar enterprise IT infrastructure commentary

© sfoskett for Stephen Foskett, Pack Rat, 2008. | EMC Atmos Versus VMware VDC-OS: Will The Real Cloud Strategy Please Stand Up?
This post was categorized as Enterprise storage, Virtual Storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.

Not to sound too much like Mr. Toigo, but I’ve been telling people this for a long time: Rather than looking to technology to solve your replication issues, consider cutting the volume of data!  Eliminating data to be replicated or adding a cheap short-distance replication target will go a lot farther than fancy link accelerators or WDM hardware.  And getting to know your data is always a good idea!

© sfoskett for Stephen Foskett, Pack Rat, 2007. | Toot toot: Cut the Costs of Disaster Recovery
This post was categorized as Enterprise storage, Personal. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.