Opinion

posted on 23 July 2008 11:17

Did the lure of server virtualization unwittingly lead to virtual machine sprawl and some other surprises?

(An opinion written by George Teixeira, Data Core President, CEO and co-founder.)

It’s not uncommon. The short term gratification from freeing rack space and lowering the electric bill soon gives way to the realization that all these VMs crowded in tight spaces significantly stress I/O channels, increase disk allocation complexity and compound the casualties from single points of failure. Face it, those discomforts will remain until you finish the job by virtualizing your storage. Only then will you be able to rapidly provision / migrate workloads, automatically load balance and fail over VMs, and non-disruptively backup and upgrade your equipment to attain the richer rewards of virtualization.

Physical Storage Reveals Old Shortcomings

Think how physical servers handcuffed you before you opted to virtualize them. Now take a look at your storage. Seeing any similarities?
Like their computing brethren, the confining sheet metal enclosure of physical storage devices prevents their contents from moving between disk arrays. When those drives aren’t fast enough or big enough to keep up with the newly concentrated loads, migrating their data to a faster drives is no small undertaking. It means downtime, lots of data copying and prayers that all dependencies have been accounted for.

What about a hardware glitch or a leaky roof that once caused an isolated disk array to take down one or two programs? Many more applications are now co-dependent on the damaged unit. Even when all the hardware pieces are working properly, piling on previously separate workloads on shared disk channels and spindles will reveal unexpected bottlenecks.

Don’t misunderstand me. I’m not recommending that you swap out your disks for really expensive high-end “intelligent” shared SAN storage. Instead, I’d suggest using a more effective and economical software approach to virtualize existing storage resources as you’ve done with the servers. In other words, take steps to overcome disks’ inherently hard-wired, mechanical packaging limitations through storage virtualization. That’s exactly what DataCore Software helps you do. Its storage virtualization software takes over where server virtualization leaves off.

Portability & Generality: Virtual Machines + Virtual Connections + Virtual Storage

To put it in perspective, hypervisors achieve portability and generality by treating disk drives as primitive objects where snapshots and other state information are kept alongside application and system data. In order to migrate system state, redistribute VMs, or fail them over, servers in the same pool must share storage repositories. Enter the SAN.
Ethernet-based iSCSI protocol is the familiar and pervasive SAN favourite, perfectly suited for VMs and virtual disks undergoing constant reconfiguration. It virtualizes disk channels allowing them to be frequently severed and reconnected without having to change the wiring. Fibre Channel is another option for heavy duty, very high-performance scenarios. However, it comes at a higher price and requires more conscious physical layout, more elaborate host bus adapters, switches and specialized networking skills.

Virtual Storage and Virtual Machines of the Same Class Maximise Asset Flexibility & Productivity

DataCore software does its magic on top of the SAN, first ensuring LUN compatibility by imitating real disks, and then super-imposing resilient, software-configurable properties well matched to the fluid nature of virtual machine environments. For starters, its software transparently pools disk space from dissimilar storage equipment and replicates it in real time between physically separate equipment for the highest availability. It can even run on a virtual machine on the same physical server adjacent to application VMs.

Then it gets really interesting. These virtual disks, like their VM counterparts can be easily and non-disruptively migrated from one disk array to another, regardless of make or model, making hardware refresh easy. Likewise, they may be transparently mirrored between separate unrelated disk enclosures to survive major failures or maintenance outages without a hiccup. Same goes for point-in-time snapshots. Virtual disks can even be remotely replicated between a primary array and a low-end device to achieve affordable Disaster Recovery between unlike equipment across distant sites. What a great way to keep that leaky roof or the flood that follows from completely crippling your main computer centre.

Equally important, DataCore’s storage virtualization software facilitates unique services like physical-to-virtual machine migrations without the usual wait-on-copy delays. Lacking their software, you would need to rely on multiple cumbersome and time consuming point-solutions. Working hand-in-hand with the server and desktop virtualization ISVs, DataCore is adding new attributes and services best rendered centrally. Their universal approach handles all the popular operating systems and disk storage variations.

Virtualization Demands I/O Performance Acceleration

Although many resemblances exist between server and DataCore’s storage virtualization, there is one important difference. Unlike hypervisors, DataCore adds no overhead on I/O transfers. Rather, it harnesses servers’ high-speed CPUs and memories to accelerate reads and writes to disks through intelligent caching. For best results, you configure the software on appropriately sized servers paired for redundancy. This completely offloads caching and spreads workloads across the SAN. Then when your demands grow or your equipment ages, you simply move the software to a more powerful server. You can’t do that if the virtualization intelligence was hardcoded and discarded with the hardware.

Complete What You Started - Virtualize Top to Bottom

Our advice, then, is to layer in the complete software virtualization stack uniformly from the server down, through the SAN and onto the storage pool. Then sit back and enjoy the robust, adaptable computer operations that you’ve been seeking.

An opinion written by George Teixeira, DataCore Chief Executive Officer, President and Co-Founder.