Database Reference
In-Depth Information
Client
Coallocation Requests
HARC
Acceptors
Phased commit protocol
Resource Manager
Resource Manager
Resource Manager
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EnLIGHTened NRM
kite1.enl-comp.org
Figure 4.6
HARC architecture. NRM
=
network resource manager.
Transaction Manager process that you find in the classic
two-phase commit
protocol
56*
with multiple, replicated processes known as
Acceptors
.
†
The over-
all system makes progress as long as a majority of Acceptors remain opera-
tional. By deploying sucient Acceptors, it is possible to construct systems
that have a very long mean time to failure, even if the mean time to failure
of each individual Acceptor is quite short.
‡
The HARC Architecture is shown in Figure 4.6. To reserve resources using
HARC,
1. the client makes a request, for example, from the command line, via the
Client API,
2. the request goes to the HARC Acceptors, which manage the co-
allocation process, and
3. the Acceptors talk to individual resource managers, which make the
individual reservations by talking to the underlying scheduler for their
resource.
HARC was designed so that it could be extended by the Grid community to
handle new types of resources, without needing modifications to the existing
code. Specifically, the required steps for extending HARC to handle a new
resource type are designing the description of the new resource type (XML);
*
Or see: http://en.wikipedia.org/wiki/Two-phase-commit protocol. Accessed July 16, 2009.
†
This terminology comes from the Paxos Consensus algorithm,
55
upon which Paxos Commit is
based.
‡
Let us conservatively assume that the mean time to failure (MTTF) of a single Acceptor is 1
week, and that following a failure, it takes an average time of 4 hours to bring the Acceptor
back online. Then, a deployment with seven Acceptors would have an MTTF of over 10 years
60
[Sec. 2.3].
