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bluesky - the three-services model

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Subject: Global-Scale Distributed Storage Systems

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  • From: Wei Dai <weidai AT eskimo.com>
  • To: Global-Scale Distributed Storage Systems <bluesky AT franklin.oit.unc.edu>
  • Subject: the three-services model
  • Date: Fri, 16 Feb 2001 01:17:02 -0800


I have been assuming a storage system design that decomposes into three
services:

1. name lookup service: maping user-friendly names/URLs to content-hash
based ids
2. data location service: maping content-hash based ids to storage servers
(network addresses and data transport protocols) that can deliver the data
3. data transport service: actually obtaining content from a storage
server given its address and a content-hash based id

This results in two levels of indirection. Some current systems seem to
have only one level, either

a. combining (1) and (2), so that a name is mapped directly to a storage
server, or
b. combining (2) and (3), so that storage servers are addressed by
content-hash base ids.

Having an extra level of indirection allows problems with both (a) and (b)
to be avoided. The problems with (a) are that the storage server has to be
trusted, and that there is waste if the same data object goes by several
names in different namespaces and is stored on multiple servers. The
problems with (b) are that if a data object changes, it would have to be
relocated to a different server, and that servers have little flexibility
in choosing what to store.

Are there proposed designs that do not fall under the three-services
model?




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