On Jun 2, 2009, at 7:04 PM, Miles Waller wrote:
> 3. ZRS
> If I'm right, ZRS still has a limitation in that there is a single  
> server
> for writes.



> Having read the factsheet, I'm a
> bit unsure as to how it is functionally different from ZeoRAID - can  
> anyone
> explain?

I'm not very familiar with ZEORaid, but, I think ZEORaid replicates
during transactions. That is, it writes to each replica at the same
time it writes to the main storage.  In ZRS, replication is
asynchronous from writes.  This means that transactions only have to
wait for writes to be completed on the main storage.
ZRS also support chaining replication, meaning a secondary can
replicate from another secondary.  For example, we typically have off-
site secondaries that replicate from an on-site secondary.

Note that ZRS has been used for years in large-scale critical

Also note that ZRS 2, which we've been using in production for more
than 2 years doesn't use spread and is much easier to configure and
more flexible than earlier versions.

See http://www.zope.com/products/zope_replication_services.html for  
more information.


Jim Fulton
Zope Corporation

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