[Zope] Re: Zeo as a Zeo Client

[Gerhard Schmidt]

On Tue, May 02, 2006 at 10:23:40AM -0400, Tres Seaver wrote:
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> Gerhard Schmidt wrote:
> 
> > I try to reduce the load of the line between the backup Computing Center 
> > and the Mainsite by having a zeo server as Proxy between the zope server 
> > at the backup site an the ZEO at the main site. 
> > 
> > Secound part is that the zeo at the backupsite can easily reconfigured in 
> > a normal ZEO when the mainsite is offline. So I don't have to reconfigure 
> > all zeoclients at the backupsite. The Data.fs is copied  every hour to the 
> > backup site so that a have an up to one our backup of the data.fs in case 
> > of a desaster at the main site. 
> > 
> > A configuration like that is described in the Zope Book on page 230. 
> > 
> > Besides I have found that with a growing number of zeo clients the Zeo 
> > server gets slower but neither the CPU nor the Harddisk IO is at the limit. 
> > We have a load of 0.2 to 0.3 and disk IO arrond 2-3 MB/sec. We have 12 
> > zeoclients at the moment and 12 more are planed for the backup site. 
> 
> I would look for a replication strategy to create your "intermediate"
> storage server:  the setup you are trying is not supported by the
> current ZEO setup.  Such strategies include:
> 
>   - Zope Corp's "Zope Replication Services" product, which keeps the
>     "secondary" storage servers synchronized with the primary via
>     the "spread" toolkit.
> 
>   - DirectoryStorage can be used to do replication via rsync.
> 
>   - Another possibility would be to use 'repozo' to create deltas
>     on the primary, and then propagate them to the secondary via
>     rsync, then apply them via 'repozo'.

I have never said that I want to have an realtime replaication. All I 
want is a ZEO at the backup site that forwards the request to the main 
site. Thats to provide a single point where i have to change the 
configuartion when a desaster at the main site happens. I simply don't 
want to change the configuration of all zope server at the backup site 
which are 12 at the first step an will grow as needed. 

As I said. The is a notable drop in perfomance with growing number auf 
connected clients. even if the clients aren't fetching objekts. I think 
this is becaus auf the growing invalidation overhead. We have a site 
with many write requests. So I hoped when i have a second zeo that the 
performance loss can be reduced. That's the second reason for the for 
this setup. 

As i figured that the cache is implemented in the zeoclient not in the 
zope server itself i thought ist might get me some proxy capabilities. 
But thats whould have been the sugar on the Top nothing realy needed as 
we have a 1 GBit connect between main and backup site. 

The question is why is it impossible to run a zeo as a zeoclient. I can 
setup a zeo with a zeoclient storage i See teh invalidations coming from 
the backend zeo. So this part works. The part with the client connect 
works also. Just the connect between both is missing. And as i said 
such a config is descibed in the Zope Book 2.5 version on page 230. 
Why has the support for such configurations droped in newer versions. 

We are planing to purchase ZRS later this year to setup an automatic 
failover. But as mentioned here. We can't use the ZRS backup servers 
when running in normal mode becaus they are read only. So I need an setup 
wer I can run a normal zeo in zeoclient mode when the mainsite is online. 
This zeo will be shutdown and replaced by the ZRS backup when the mainsite 
goes down. Otherwise i have to mess with IP takeover and other very messy 
strategies. I'm trying to get this as simple and as stable as possible. 

Bye 
	Estartu    

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Gerhard Schmidt    | Nick : estartu      IRC : Estartu  |
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