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2010 Shines a Light on Mistaken Storage Assumptions

What do Virtualization and Cloud executives think about 2010?  Find out in this series exclusive.

Contributed article by Mark Davis, CEO, Virsto Software

2010 Shines a Light on Mistaken Storage Assumptions

The Sins of the Past

In 2010, the virtualization world will start dealing with a decision collectively made by the industry when virtual servers were born: to treat storage under virtual servers the same as physical servers.

It was a convenient compromise.  As long as we didn't push virtual infrastructure too hard, it seemed to work.

But that compromise came at a price.  Users saw virtual servers consuming up to 25% more storage than equivalent physical servers.  I/O performance issues that never happened on physical servers choked boxes running several VMs.  The complexity of storage provisioning and backup was compounded by virtualization.  Most cruelly, we found that all the money saved by virtualizing servers was spent on additional storage hardware and software.

The Root of the Problems: Bad Assumptions

In the 1800s, physicists began to realize their subatomic models were wrong because they were based on the plausible but flawed assumption that mechanics at tiny scale operated just as we observe for larger objects.  It turned out that interactions of the very small defied common sense.  The superior quantum mechanical model was invented.

The flaw of the false premise is often hidden, because our assumptions can be so embedded we don't realize we have them, let alone that they're wrong.  Such is the case in the storage industry.  Here are a couple of the flawed technical presumptions that have carried over from physical to virtual servers.

Assumption:      Clones & snapshots are second class citizens
Virtual Reality:   Almost every OS image is a clone

Snapshot and cloning technologies have been around a long time, relying on assumptions that don't pan out in the virtual world:  Snapshots are the exception, not the rule.  Snapshot performance is not as important as for base images.  It's fine if snapshot performance degrades over time, because it won't live long.

In the VM world, quite the opposite is true.  We end up with hundreds, even thousands of VM images, and we don't create them temporarily for backup.  We want to run them in production for a long time.  Because there are so many images built from golden masters, we want to use space efficient snapshots, but their characteristics make them unfit for production applications.

Assumption:      Server software does a decent job of optimizing I/O
Virtual Reality:   The VM I/O blender

For decades, device drivers, volume managers, filesystems and databases have optimized the I/O streams sent to disk subsystems.  This is based on the still-true premise that random I/O to a spinning disk is two orders of magnitude slower than sequential I/O.

But the hypervisor layer jumbles streams from multiple guests, resulting in the well known VM I/O blender that can reduce physical server output by 80%.

The Risk of Believing Old Assumptions

There are significant mistaken assumptions besides those listed above, but from these examples a pattern emerges.  Moving from the old world of physical servers to the new reality of virtual servers requires new thinking about storage.

Sometimes, it makes sense to apply tried and true technologies to new problems.  Keeping invariant part of the technology as we innovate in a new area can make the initial transition easier.  Early automobiles used the same kinds of wheels as horse drawn wagons, even after invention of the pneumatic tire.  That was fine when cars were rare, slow moving novelties.  But if car wheels didn't become air filled rubber bladders, the history of transportation would be very different.  The assumptions of the wagon wheel - that passenger comfort was unimportant, the vehicle was slow, roads were filled with sharp rocks, and a cleverer wheel couldn't be invented - turned out to be pessimistic.

Old assumptions about storage are holding back virtual servers.  We aren't traveling nearly as far, fast or comfortably down the virtual road as we should be.  Virtual servers in 2009 are like the auto before introduction of the air cushioned tire.  Now that virtualization is no longer an unusual novelty, the storage wheels of virtualization could use some air.

Storage for virtual servers is overly complex, causes IT professionals to make uncomfortable compromises, and costs too much.  In 2010, the virtualization industry will start dealing with the flawed assumptions embedded in today's storage technologies.

About the Author

Mark Davis, CEO, Virsto Software 

Mark has been at the center of the networked storage and virtualization revolution since day one. He launched the first Fibre Channel disk array in 1994, and was instrumental in growing Sun Microsystems from a non-player to the largest Unix storage vendor within five years. After a stint as VP of marketing at industry icon StorageTek, Mark repositioned ConvergeNet from being yet another RAID vendor to the inventor of SAN-based storage virtualization, leading directly to Dell's purchase of the company for $340M. After playing an instrumental role in the IPO of professional services software vendor Evolve Software, Mark returned to the storage industry, working on multiple virtualization projects. Before co-founding Virsto, he was CEO of storage resource management vendor Creekpath Systems, where he engineered a successful acquisition by Opsware (now HP).

Published Tuesday, December 08, 2009 5:54 AM by David Marshall
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