[Zope] ZEO with Multiple Storages

[Jonathan]

----- Original Message ----- 
From: "Martijn Pieters" <mj at zopatista.com>
To: "Jonathan" <dev101 at magma.ca>
Cc: "Brian Brinegar" <brinegar at ecn.purdue.edu>; <zope at zope.org>
Sent: Thursday, September 14, 2006 2:54 AM
Subject: Re: [Zope] ZEO with Multiple Storages


> On 9/14/06, Jonathan <dev101 at magma.ca> wrote:
>> If you mean having zope commit a single transaction to multiple storages,
>> then 'vanilla' zope won't do it (Zope Corp has a commercial product 
>> called
>> ZRS which does this type of thing).
>
> No, that's not true. ZRS is used to create hot read-only or stand-by
> copies of a ZEO server (and all storages within such a server are
> copied).
>
> One ZEO server can deal with multiple storages just fine. Transactions
> involving multiple storages commit just fine.

Yes and No!

Yes: a single zeo server can deal with multiple storages (ie. a storage can 
contain mount points to other storages)

Yes: if a single transaction creates/modifies multiple objects and each of 
those objects is stored in a different storage (all storages 'served up' by 
a single zeo server), then the single transaction will commit those objects 
to their respective storages with no problem. (however, there are little/no 
performance improvements in this scenario)

No:  if a single transaction creates/modifies a single object, that single 
object can not be stored over multiple storages (ie. you cannot achieve RAID 
'disk striping' type of performance improvements)


However, that being said there may be some improvement, if the application 
is disk-bound, by giving each storage its own disk subsystem (never tried 
this myself, but it may buy some small performance improvement).  For the 
cost/effort involved I would stick to having a single zeo server 'serve up' 
a single storage, and have each zeo server on its own hardware platform 
(much more scalable, easy to implement).


Jonathan