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4th USENIX Conference on File and Storage Technologies—Abstract
Pp. 295–308 of the Proceedings
VXA: A Virtual Architecture for Durable Compressed Archives
Bryan Ford, Massachusetts Institute of Technology
Abstract
Data compression algorithms change frequently, and obsolete
decoders do not always run on new hardware and
operating systems, threatening the long-term usability of
content archived using those algorithms. Re-encoding
content into new formats is cumbersome, and highly undesirable
when lossy compression is involved. Processor
architectures, in contrast, have remained comparatively
stable over recent decades. VXA, an archival storage
system designed around this observation, archives
executable decoders along with the encoded content it
stores. VXA decoders run in a specialized virtualmachine
that implements an OS-independent execution environment
based on the standard x86 architecture. The VXA
virtual machine strictly limits access to host system services,
making decoders safe to run even if an archive contains
malicious code. VXA's adoption of a "native" processor
architecture instead of type-safe language technology
allows reuse of existing "hand-optimized" decoders
in C and assembly language, and permits decoders access
to performance-enhancing architecture features such
as vector processing instructions. The performance cost
of VXA's virtualization is typically less than 15% compared
with the same decoders running natively. The storage
cost of archived decoders, typically 30Ð130KB each,
can be amortized across many archived files sharing the
same compression method.
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