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Overland Storage’s Rationale for Configuring Its REO Backup Appliance as a VTL

Any time one looks at midrange backup appliances, the appliances are almost always NAS based. When configured this way, the backup appliance is attached to the local LAN, it appears as a filer server to the backup server and files are backed up to a folder on that appliance. Though I initially called to speak to Overland Storage’s Senior Product Manager, Jeff Graham, about REO’s Dynamic Virtual Tape (DVT) technology, I first wanted to get some clarification on why Overland Storage’s REO-series appliances are configured as Virtual Tape Libraries (VTLs) rather than as a NAS-based appliance.

Jeff provided a couple of reasons as to why Overland Storage currently configures its REO-series appliances as VTLs:

The first reason has to do with performance. Overland Storage has found that its VTLs consistently outperform NAS-based appliances. On NAS-based appliances you have to introduce a file system on the appliance which consumes some server overhead (processing and memory) that a block-based VTL does not consume. However, the larger benefit of using a REO is that it is optimized for storing the large sequential blocks of reads and writes found in backup traffic. Using a NAS, these blocks will fragment over time as the system distributes these blocks of data across the back end disk drives. Using a REO-series VTL, all of the blocks of data are kept together on a specific virtual tape cartridge that helps prevents this type of fragmenting from occurring.

The other reason is manageability. Using a NAS-based backup appliance, folders are created on the appliance’s file system that is then used to store the backup data. The problem that can emerge in this scenario is that as if and when the folder fills up with data, the backup job can fail or hang. To allow the backup job to continue, administrators may need to increase the folder’s size, manually direct the backup software to backup the data in another folder or manually give the OK to the backup software to overwrite older data in that folder.

Using a REO-series VTL, administrators have a couple of options within the backup software that minimize the likelihood of backup job failures. They can configure the backup software to migrate data from virtual tapes to physical tapes so as the REO VTL fills up, the backup software recognizes this and automatically moves the data from virtual tape to physical tape and then deletes the data on the virtual tape. Alternatively, companies can add more disk capacity to the REO and create more virtual tape cartridges for additional storage capacity.

Bottom-line, using a REO VTL companies do not need to change their backup structure. The backup software recognizes and treats the REO VTL like a physical tape library which minimizes the number of changes that companies need to make their backup infrastructure.

Now, having said all of this, Graham says that Overland Storage is investigating the possibility of adding a NAS option to their backup appliance. The rationale behind this move is that despite the fact VTLs are better suited for backup, there are still market forces at play. A NAS-based backup appliance is simpler for companies to understand since it does not require Overland Storage or its resellers to explain what a VTL is or how it. However, Graham did not indicate if Overland Storage actually plans to move in this direction or, if they are, when such an appliance might be released.

In a future blog entry, I’ll delve more deeply into Overland Storage REO’s DVT technology, how it works and what makes it unique in the market place.


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