Chris Huebsch wrote:
On Wed, 3 Jan 2007, Chris Huebsch wrote:
AFS does not provide hot-standby or failover.
Perhaps I should clearify that a little bit.
In some special cases, AFS can do that too. But it requires that those
Data is strictly read-only.
This read-only data has to be created from read-write data (this is
called "release" in AFS-speak). This process takes some time, so it is
neither recommended nor feasible to do that release in very short
intervals.
The AFS read only replicas are updated from their parent RW volume.
Unless "-f" is specified on the "vos release <volume name or ID>"
command line the update is 'whole file incremental' -- only files that
have changed are 'shipped.'
Time required for a vos release therefore varies considerably from one
volume to the next. It also varies with the number of update sites and
the bandwidth available between them.
Even when no file has changed in the RW volume the 'vos release' process
has to confirm and this requires some time.
"Instant" replication is not something to expect from AFS.
AFS will provide near-instant failover to replicated, read only data.
If your purpose is instant failover to read/write data then AFS does not
qualify, as Chris says.
Kim
Chris
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