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Much of the functionality promised by virtualization isn't new. What is new is that this functionality is now offered at the network layer. Functions like volume management and replication work well at the host and storage layers. By pushing these out to the network, you can avoid the constraints of a single platform/vendor and benefit from consistent manageability across a range of heterogeneous platforms. Let's consider some of the services provided by virtualization and their applicability to the storage network:
- NETWORK-BASED VOLUME MANAGEMENT. While never fully appreciated in Windows environments, anyone who has dealt with large Unix servers is likely a big fan of LVMs. But with a host-based volume manager, efforts must be duplicated for each server; and, depending on the specific environment, multiple products with different management interfaces may be required. Providing this functionality at the network layer can provide consistency and simplify deployment and ongoing management. It may also save on licensing costs (when volume management isn't bundled with the OS). Volume management can be viewed as the foundation app for network-based virtualization and, as such, this functionality is provided by EMC, Hitachi Data Systems (HDS), IBM and others in their virtualization products.
- CLONING AND SNAPSHOT. There's considerable benefit to
- creating point-in-time copies at the network layer. Split mirrors or snapshots for backup, development or testing can be created on low-cost storage volumes. Managing this capability on a SAN-wide basis, and allocating and reusing storage from a common pool, leads to simplified management and consistent application of policies. Enabled largely by LVM capability, this functionality is available in some form with all virtualization products.
- REPLICATION. At first glance, replication at the network layer should be a no-brainer, at least conceptually. Replicating heterogeneously has a number of benefits, not the least being potential hardware cost savings. Depending on the vendor's virtualization approach (and willingness to potentially displace other products), however, replication may not be available. Replication, in general, is a touchy area and there are real tradeoffs between the available options.
- DATA MIGRATION. One of the great promises of virtualization is increased flexibility. Network virtualization can speed provisioning and simplify data migration. We've seen cases where new storage array deployments were delayed by up to a year because of challenges related to migrating from old servers and arrays. Data migration alone may justify virtualization, particularly in environments where large-scale retiering of apps is underway. The LVM capabilities within most virtualization products provide the means to transparently migrate data from one storage device to another without reallocating logical unit numbers or reconfiguring servers.
- FILE-SYSTEM AGGREGATION. Virtualization doesn't apply only to block-level data. There are also beneficial applications of virtualization relating to file-level access within the NAS realm. The presentation of a consistent global file system can simplify provisioning and management of environments with lots of NAS devices and many shared CIFS or NFS file shares. This functionality is available via software or through appliances from Acopia, EMC (Rainfinity), NeoPath (File Director), Network Appliance (Virtual File Manager), NuView (StorageX) and others.
- THIN PROVISIONING. Capacity planning and improving utilization are significant challenges in storage management. The ability to "overprovision" or "thinly provision" storage is a virtualization technique that holds enormous potential. By eliminating the padding of storage allocation requests in every environment, this could be the "killer app" for virtualization. 3PAR is often associated with this capability, but it's becoming available at the network virtualization layer. Specifically, NetApp provides overprovisioning with the FlexVol feature on its dedicated storage platforms and its V-Series NAS gateways. The V-Series devices support storage from Hewlett-Packard, HDS and IBM.
Virtualization will eventually become widespread because the business case is so compelling. While we can point out the many administrative benefits, virtualization provides two huge cost-savings functions to business: it furthers the commoditization of infrastructure and improves the liquidity of capital assets. For servers, much of the attraction of products like VMware is the masking of physical platforms making it easy to replace server A with server B. Likewise, storage virtualization will lead to further commoditization of storage platforms, particularly in the midrange. As far as asset liquidation, whether dealing with lease rollovers, technology refreshes or other business events, virtualization makes it significantly faster and easier to move hardware in and out of the environment.
None of these virtualization techniques is without its challenges. Reducing complexity in one area often increases complexity in another. Virtualization can help to automate processes, but those processes must be fundamentally sound and well thought out to begin with. Simplifying storage provisioning and masking the physical infrastructure can create new management issues. However, the rising costs associated with storage management demand automation efficiencies. These efficiencies can only be achieved through some type of abstraction of the logical from the physical, which means virtualization.
This was first published in March 2006