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sql server clustering : High availability, VMWare and remote sites.


Charles Deaton
1/11/2007 8:17:29 AM
We are starting to look into a high availability solution to ensure
operation of our business in the event of a localized disaster
(i.e.. building fire). We are planning on a remote site, maybe
25 miles away, that will provide virtual servers and resources via
VMWare. We will need, among other things, to have a warm
stand by MSSQL 2000 server up and running. I'm aware of the
common solution such as log shipping, mirroring in 2005 and
replication. We do not want to upgrade to 2005 so mirroring is
not an option. We will need to be able to fail back to the primary
MSSQL server with little or no intervention when the disaster
has been resolved so replication is not an option. Our databases
are used for a hybrid OLTP system with several thousand
transactions per second. Data loss needs to be kept to a
minimum. Failover and fail back should be seamless
(No data loss except opened transactions?).

We are looking at DoubleTake, NeverFail, XOSoft and
Goldengate products. It seems like some play better with
VMWare than others. We have not looked closely at Symantec,
EMC or SteelEye but am aware of that they offer possible
solutions as well.

If anyone has any hands on experience with a solution similar
to what we are looking into we would appreciate your comments.

Thanks,
Charles Deaton
Hilary Cotter
1/11/2007 12:35:23 PM
Use bi-directional transactional replication. Change your identity seeds to
odd on one side, even on the other. This way you never have to worry about
failing over or failing back and synchronization as both sides are live
simultaneously.

The only issue with this is client re-direction in the event of a failover.

--
Hilary Cotter

Looking for a SQL Server replication book?
http://www.nwsu.com/0974973602.html

Looking for a FAQ on Indexing Services/SQL FTS
http://www.indexserverfaq.com



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Edwin vMierlo
1/11/2007 4:33:25 PM
Charles,

for a "no IO lost" solution on EMC Symmetrix, I can highly recommend EMC
SRDF/CE 2.2. This is a Geocluster solution.
It uses EMC SRDF/S technology to ensure all data is synchronised (to the IO
level). You can built your cluster, half of the nodes in your primary
datacenter, half of the nodes in your secondary datacenter.

It will failover your cluster to your secondary datacenter (to the
un-trained eye, it is *just* a cluster)
AND
It will failback your cluster to your primary, as simple as clicking "move
group" in Cluster Administrator, once your primary site is back up, disaster
over.

I don't think it will tie in with your VMWare limitation, but for a High
transacting db (as you mention several thousands of transactions per second)
I am not sure if a virtual server would cope with that anyway.

I have been running many SRDF/CE solutions for several years, but to be
fair: I have not ran other geocluster solutions, so my opinion is probably
biassed a bit. If your are not running EMC Symmetrix storage, then this
solution could be a bit costly, as a minimum you need two Symmetrix storage
units and obviously the FC-fabrics and FC interconnects between the two
data-centers.

rgds,
Edwin.


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Anthony Thomas
1/14/2007 11:11:31 PM
What Edwin is referring to is termed "stretch clustering." We too have been
running Remote Disk Mirrors successfully with only bandwidth issues as the
down side.

In stretch clustering, you will need to maintain a "warm" DR site and is
built on top of remote mirroring. With remote mirroring alone, you can
maintain a "cold" site.

You could also run SRDF/A (asynchronous). This overcomes some of the disk
mirroring bottlenecks with only a minor increase in risk for data loss (it
allows 1 pending IO in the queue without remote commit instead of dual
commit associated with synchronous mode). Do not let any storage
managers/technicians sell you on the idea of Adaptive Copy. The technology
does NOT preserve the write-ordering necessary to maintain the WAL (write
ahead logging) protocol necessary to maintain database transaction ACID
properties.

You will not be able to SAN replicate if one host is real and the remote
host is virtual.

SQL Server 2000 High Availability Series
Implementing Remote Mirroring and Stretch Clustering
http://www.microsoft.com/technet/prodtechnol/sql/2000/deploy/hasog05.mspx

Requirements for SQL Server 2005 and SQL Server 2000 to support remote
mirroring of user databases
http://support.microsoft.com/kb/910716

Best of luck.

Sincerely,


Anthony Thomas


--

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daveberm
1/15/2007 7:18:48 AM
SteelEye works great with Physical to Virtual clustering of SQL Server.
If you contact us, we can give you great SQL Server reference
accounts.

David A. Bermingham, MCSE, MCSA:Messaging
Senior Systems Engineer
www.steeleye.com

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