[THIN] Re: high availability
- From: "Ron Oglesby" <roglesby@xxxxxxxxxxxx>
- To: <thin@xxxxxxxxxxxxx>
- Date: Tue, 11 May 2004 11:36:34 -0500
There are two ways to do it. Merge replication (not supported by Citrix) and
Transactional replication. The change to a subscriber (remote SQL DB) is
really passed to the Publisher (master copy) to verify that there is no
conflict with the change. The change is incorporated at the publisher, then
replicated back to the subscriber. It's a really fast process and works
pretty well in most cases. It also gives you the "look" of having writable
copies in all locations. If the publisher is down though you cant change the
DB but you can get into the CMC and look around etc.
But you still have to turn one of the DS DBs into a publisher if you are not
going to be able to recover the primary.
Ron Oglesby
Senior Technical Architect
Microsoft MVP - Windows Server
RapidApp, Chicago
Mobile 815 325-7618
Office 312 372-7188
e-mail roglesby@xxxxxxxxxxxx
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf
Of Steve Greenberg
Sent: Tuesday, May 11, 2004 11:23 AM
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: high availability
Seems to me that if you have farms around the world depending on a =
single
data store that it would been to be fault tolerant in a true =
active-active
scenario, i.e. all instances have all the information and can accept =
reads
and writes. Is this possible with MS SQL???
Steve Greenberg
Thin Client Computing
34522 N. Scottsdale Rd. suite D8453
Scottsdale, AZ 85262
(602) 432-8649
(602) 296-0411 fax=20
steveg@xxxxxxxxxxxxxx
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On =
Behalf
Of Lilley, Brian
Sent: Tuesday, May 11, 2004 9:03 AM
To: 'thin@xxxxxxxxxxxxx'
Subject: [THIN] Re: high availability
also, if you had four marooned sites with read/write replica's of the =
Data
Store, how would you recover from this in terms of re-syncing the =
databases?
Thanks,
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx]On
Behalf Of Lilley, Brian
Sent: 11 May 2004 16:49
To: 'thin@xxxxxxxxxxxxx'
Subject: [THIN] Re: high availability
Big Ron,=20
When you say "SQL server", I assume you are referring to SQL based
relational database servers in general and not specifically to MS SQL
server.
Ok, now I may be being totally over-pessimistic about =
publisher/subscriber
replication here, but do you think it would be feasible to operate =
something
like the following: as part of a controlled maintenance window, point a
server to the master copy of the datastore for the duration of updates =
to
the data store? =20
Are the benefits gained by having a simpler replication topology =
outweighed
by the amount of effort to provide a maintenance schedule like above. I =
am
ultra paranoid about a single global farm replicated between 8+ servers.
Would you trust the publisher/subscriber model for 8+ Data Store global
single farm? Do you trust DSCHECK? Am I worrying too much? =20
thanks in advance,
Brian
=20
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx]On
Behalf Of Ron Oglesby
Sent: 11 May 2004 13:46
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: high availability
Well. One thing that I can say is any location you have a Citrix server
using a SQL server the DB should be read/write/. Now what do I mean by =
that?
I mean that you should be using a publisher/subscriber model with
transactional replication/immediate updating. This will allow the =
changes
from servers talking to the subscriber to be pushed up to the Publisher
(master) written into the DS, then replicated to all servers.
The trick with this is that any servers online are going to have changes =
(of
some type, print drivers added, hotfixes added, etc). And these changes =
need
to update the DS. So I would not use a straight push for any SQL server =
with
hot online servers connecting to it. Now to use one as a COLD SQL server =
you
can do that. But lets assume a site loss. You have lost 50-75 servers in =
one
site along with the Datastore. Now you have a shipped Database to =
another
site. And you are going to start installing servers into that site to =
get
you up to capacity. All the shipping did was handle your published apps =
and
licenses for the most part, since the 75 servers are "gone" but remain =
as
ghosts in the DS and you still have to get a bunch of servers on line.
Get it?
Ron Oglesby
Senior Technical Architect
Microsoft MVP - Windows Server
=20
RapidApp, Chicago
Mobile 815 325-7618
Office 312 372-7188
e-mail roglesby@xxxxxxxxxxxx
=20
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On =
Behalf
Of Lilley, Brian
Sent: Tuesday, May 11, 2004 3:10 AM
To: 'thin@xxxxxxxxxxxxx'
Subject: [THIN] Re: high availability
Big Ron,
Thanks again for your response.
I will be replicating a master read/write copy of the database to =
perhaps 5
major regional sites and maybe a couple more at a push. =20
Again, back to the DR hot-sites, should I make a data store present =
there
also?
I guess it's a balance between reducing the complexity of the data store
replication and having a truly 'marooned' DR site available almost
immediately.
Personally, from the feelings I got from this list, I would tend =
towards
keeping the data store replication to a minimum and allowing the DR =
scenario
the Citrix grace period to restore a data store onto an Oracle box which =
is
pretty straight forward.
When I first asked about data store replication some weeks ago, I =
mentioned
replication to ten servers globally for a single farm model (and most of =
the
old timers winced slightly). I am still looking to move forward with a
global single farm with data store replication to a reduced number, prob =
5
or so... do you guys still hold the same view?
Also, can DSCHECK.EXE be trusted as a signature for health on the IMA =
data
store?
best regards,
Brian
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx]On
Behalf Of Ron Oglesby
Sent: 10 May 2004 20:07
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: high availability
Simple answer. No it does not need to be clustered. Complicated =
answer...
maybe.=20
I mean the real trick is how many (and what type) of changes will you =
need
to make if it is unavailable. In most cases your answer will be none. We =
can
operate without making changes to the DS for a couple of days. If that =
is
true then you don't need the cluster.=20
Replication or shipping of the DB/Logs is needed though for any type of =
DR.
Of course there are drawbacks to this too. I mean If you use =
transactional
replication then when the primary is gone you cant make changes anyway
(until you turn the subscriber into the publisher). So it all depends.=20
Hey, I can come out and work on this with ya. It sounds fun and right up =
my
alley.=20
Ron Oglesby
Senior Technical Architect
Microsoft MVP - Windows Server
=20
RapidApp, Chicago
Mobile 815 325-7618
Office 312 372-7188
e-mail roglesby@xxxxxxxxxxxx
=20
-----Original Message-----
From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On =
Behalf
Of Lilley, Brian
Sent: Monday, May 10, 2004 8:39 AM
To: 'thin@xxxxxxxxxxxxx'
Subject: [THIN] high availability
Chaps, I need to draw on your experiences again...
Does the primary IMA Data Store really need to be clustered, or is this =
more
complication than it is worth. KISS principle, etc.?
I appreciate that high availability is important, but isn't the =
integrity of
the database even more important. Without a Data Store, what's the =
worse
that could happen during the 96 hours, you can't make changes??
If something was seriously wrong the master IMA Data Store cluster node =
A,
would we want the second cluster to take over? Is there not a further
chance of corrupting data by having this nice-ity??
If the Data Store becomes unavailable, presumably an app server can =
still
boot from the contents of the LHC?
thanks,=20
Brian
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