The "Infinite" Challenge of ProStor Systems' InfiniVault Archiving Appliance; Part 1 of 2

Infinite. That's the number of files that the file system on ProStor Systems' InfiniVault archiving appliance can theoretically support. The problem with InfiniVault supporting an infinite number of files is how does that work under real-world conditions and how does anyone verify that number in order to have some level of assurance that it holds up?

In ProStor Systems case, verifying its claim is more important than in the case of most other disk vendors since its disk-based InfiniVault also supports infinite storage capacity. ProStor Systems accomplishes this rather unusual feat for a disk-based system by using removable RDX disk cartridges. This gives InfiniVault the same infinite storage capacity feature that tape libraries possesses.

The InfiniVault is available in three models, Model 3, Model 30 and Model 100 that spec out at 1.6, 11 and 39 TBs respectively, with their capacity numbers based upon the largest capacity RDX disk cartridges available. However the total amount of storage capacity any one of these models can actually manage is theoretically infinite since users can remove RDX cartridges once they are full and replace them with new, empty RDX disk cartridges, just like tape.

This situation presents the following challenges for InfiniVault's file system:

• It needs to recall files on disk cartridges even if they are not in the InfiniVault
• Since InfiniVault supports infinite capacity, it needs to support infinitely many files
• Archiving may require it file retention for an infinite period of time

 InfiniVault's file system handles the first problem in unique way. When new InfiniVault systems are sold, ProStor Systems helps its clients size the InfiniVault so it possesses sufficient disk cartridge slots so they can keep one year's worth of data on the InfiniVault without removing any disk cartridges. ProStor Systems has found that customer retrieval of archived data drops off significantly after 90 days and that the retrieval of data over a year old is almost non-existent.

By sizing the system so it holds one year of data, when its clients need to replace a full disk cartridge with an empty disk cartridge, they can replace it with a larger capacity disk cartridge. Right now the largest capacity RDX cartridge available is 300 GB but by this time in 2009, it will likely be a 1 TB cartridge. Since RDX cartridges are forward and backward compatible, companies can increase the storage capacity of the InfiniVault by just inserting a new disk cartridge which also increases each InfiniVault's slot value since it now holds more raw capacity.

In the event a request is made for a file that is on an RDX disk cartridge that is not in the InfiniVault system, the InfiniVault prompts the user to insert the cartridge back into the InfiniVault so it can retrieve the file. How time-consuming this task is depends on how well disk cartridges external to the InfiniVault are managed, where they are physically located and how many files are retrieved.

The second scenario, performing a search of all files on disk cartridges managed by the InfiniVault, is potentially more problematic since they could require retrieving and inserting all external disk cartridges managed by the InfiniVault. InfiniVault partially mitigates this search concern by indexing the content of files as they are stored and then searching this content index. However both cases would seem to call for ProStor Systems to eventually introduce an automated tape library or partner with an existing tape library vendor to provide this type of functionality for RDX, both of which they have hinted at in the past.

The problem of verifying their claim that InfiniVault supports an infinite number of files is a more complicated question to answer and will require a separate blog entry to thoroughly examine. Look for the blog entry that addresses InfiniVault's other challenges sometime later this month.

This blog entry is the first in a two-part series that looks at how ProStor Systems InfiniVault uses a file system that supports a theoretically infinite number of files to manage infinite capacity. If you have any questions, you may contact ProStor Systems through their PR representative, Judy Smith, at judys@jprcom.com.