Erfinderische Speichervirtualisierung (T0743/11)

Dateisystem-Kenner aufgepasst! In der Entscheidung T 0743/11 (Write allocation/NETWORK APPLIANCE) vom 12. April 2013 ging es um eine Erweiterung des WAFL-Dateisystems mit einer weiteren, zweiten, Virtualisierungsschicht (“virtualization layer”).

Die Kammer 3.5.01 hat festgestellt, dass das Hinzufügen einer zusätzlichen Virtualisierungsschicht für sich genommen für den Fachmann naheliegend ist (d.h. nicht erfinderisch). Nicht naheliegend — und damit erfinderisch — sei es jedoch gewesen, die speziell vorgeschlagenen “cross-layer pointers” zum Vereinfachen des Lesezugriffs zu verwenden.

Die Entscheidung enthält darüber hinaus eine interessante Aussage dahingehend, ob ein Tradeoff zwischen dem Lese- und Schreibaufwand für den Fachmann (der in dieser Entscheidung übrigens weiblich ist) naheliegend ist.

Aus der Begründung

[4.] Main request, Article 56 EPC 1973

[4.1.] Claim 1 defines a method of write allocation in which two virtualization layers (the aggregate and the virtual volumes) sit on a RAID plex. Each of them has its own space of block addresses and each maintains its own block allocation structure. When a block is allocated in a virtual volume, a parent block (which will be an inode or an indirect block) is updated so as to include the corresponding block number in the aggregate.

[4.2.] The Board and the appellant agree that the prior art WAFL system, as set out in the application, is the most appropriate starting point for the assessment of inventive step. That prior art system had a single virtualization layer, and, therefore, a single block allocation structure. The pointers in its inodes and indirect blocks were to blocks within the same virtualization layer, and it was the job of the underlying RAID system to translate those blocks numbers to its own representation.

[4.3.] In contrast to that prior art, the invention defined in claims 1 and 10 has the aggregate layered on top of the RAID system. The virtual volumes now sit inside container files on the aggregate. In effect, there are, according to the invention, two layers of virtualization. That allows a more flexible use of the underlying RAID system by the virtual volumes.

[4.4.] Such a two-layer structure is not part of the prior art WAFL system. Nor do any of the documents cited in the decision under appeal disclose one. In this respect, it is significant to note that the underlying RAID system cannot itself be regarded as a virtualization layer in the way the aggregate is. That is because the RAID system does not concern itself with block allocation structures. That is the job of the file system that makes use of the RAID system.

[4.5.] In the Board’s view, the simple addition of a new layer of virtualization would not involve an inventive step, because successive virtualization has been an important factor in the development of storage devices. Nor, once the decision to add a new virtualization layer has been taken, would the use of the same sort of block allocation structures as those already used be anything more than an obvious choice. However, the invention does more than add a virtualization layer using the same sort of allocation structures as are already in use. During write allocation, it puts (cross-layer) pointers to aggregate allocation structures in the inodes and indirect blocks of the virtual volumes. As a result, when the data are later read, there is no need to convert from the block structures of the virtual volume to the underlying block structures of the aggregate. The saving during reading is at the cost of more processing during writing, and of some storage capacity. That is part of the sort of trade-off that an engineer routinely makes, but the Board does not consider that every manifestation of a trade-off is obvious simply because the factors traded off are known. In the present case, while it would have been obvious to the skilled person to trade off ease of reading against ease of writing and cost in storage, there is nothing to suggest that she would have considered using cross-layer pointers in doing so. None of the prior art suggests cross-layer pointers at all.

[4.6.] The Board concludes that the subject matters defined in claims 1 and 10 according to the main request do involve an inventive step (Article 56 EPC 1793).

Link zur Entscheidung T 0743/11 (Write allocation/NETWORK APPLIANCE).

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