Initial filesystem design synopsis.

Matthew Dillon dillon at
Thu Feb 22 10:37:26 PST 2007

:I have a question about a specific scenario.  You mention
:multi-master, replication and off-line operation.  Suppose
:I have two machines in a replicated multi-master setup,
:i.e. each of them has a full copy of the file system to
:work with, and both have write access which is replicated
:to the partner.  This could ba a set of redundant servers,
:or maybe a desktop machine plus a notebook.
:Now what happens if the two nodes are disconnected for a
:certain period of time?  E.g. there's a network outage, or
:the notebook is taken off-line on a trip.  In such a
:situation, both nodes should still be fully functional
:with write access, of course.  Therefore, each node must
:maintain a queue of changes that need to be replicated to
:the other node as soon as the connection is restored.

    You have two options:  First, operate the cluster filesystem in
    quorum mode, where modifying operations are only allowed if a quorum
    of replication masters is accessible.  This is the most typical
    scenario.  Conflicts do not occur when using a quorum protocol.

    Second, operate the cluster filesystem in independant-operation mode,
    which is how one would have to operate something like a laptop,
    where work must be synchronized at a later date and for which 
    conflicts may occur.  In this situation conflicts must be brought
    to the attention of the user and the user must choose how to resolve

:Given your feature summary, a few interesting abbreviations
:can be made, for example:
:high-availability replicated distributed file system
:high-availability clustered replicated file system
:== HACRFS  (pronounced "hacker FS", of course)
:high-availability multi-master extra reliable file system
:The "R" can mean replicated or reliable (or robust),
:whatever you prefer, and the "E" can mean extra, eminently,
:exceedingly or exceptionally.
:Best regards
:   Oliver

    HAMMER is a good name (though I dont like the expanded acronym).
    I like HACFS better then HACRFS.

    I like HAMMER better then HACFS but HACFS's expanded acronym is


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