(Simple?) High availability question

[tleslie]

On Fri, 2007-06-01 at 21:15 -0400, Ansar Mohammed wrote:
> There are many types of HA solutions.
> 1. Load balancing: This assumes that there is little or no data to
> synchronize and basically the client connections are load balanced between
> two or more hosts. Eg: DNSRR, OpenBSD pf, Cisco  and WLBS. Typically this is
> used to load balance web servers, dns servers and firewalls.
> 
> 2. Shared Nothing: This consists of two or more physical servers connected
> back to shared LUN on scsi bus, FC SAN or iSCSI. In the Windows and UNIX
> worlds this is what "clustering" refers to MOST of the time. You can do the
> same thing on Linux/FreeBSD using scripts. This is typically how MOST
> database servers are clustered.

I disagree, i thought shared nothing means they "share nothing", and
have separate file systems.
Thats what i got out of a white paper from IBM on DB2 versus Oracle.

Now if you have a shared SAN and it a net app that has redundant 
heads and storage and fail over,
you have two or more application servers fronting a 
truely redundant "filer".

This is the way i went, all though the DB2 sol'n sure looks good. But we
needed the Netapp dual-head SAN for other stuff, so it made the 
Oracle cluster system (single shared disk array) viable, as with the
Netapp (3040), is truely a redundant SAN.

We actually had to by netapp oracle aware cluster software, so the 
netapp is taking the snapshoots that are accurate of the DB.

-tl


> 
> 3. Application Clusters: Application specific replication technology that
> replicates data and manages client connectivity. Eg: Active Directory,
> Oracle RAC, SQL Server. It can be replicated in an opensource environment
> with rsync and DNS
> 
> 4. Distributed systems: many systems working together distributing
> processing among them eg: Beowulf, PVMs, Windows Compute Cluster.
> 
> To solve your problem for high availability you should ideally use a shared
> nothing cluster for the database and DNS RR or IP Load Balancing for the web
> servers.
> 
> 
> 
> > -----Original Message-----
> > From: owner-tlug-lxSQFCZeNF4 at public.gmane.org [mailto:owner-tlug-lxSQFCZeNF4 at public.gmane.org] On Behalf Of Madison
> > Kelly
> > Sent: June 1, 2007 6:00 PM
> > To: tlug-lxSQFCZeNF4 at public.gmane.org
> > Subject: Re: [TLUG]: (Simple?) High availability question
> > 
> > Ian Petersen wrote:
> > > On 6/1/07, Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org> wrote:
> > >> I believe mysql has a replicating
> > >> server backend, although apparently that backend is much slower and has
> > >> less features than the regular one, so it is a major tradeoff there.
> > >
> > > I used to work for a place that relied on MySQL for the majority of
> > > its database needs.  I believe the MySQL dbs were all replicating in
> > > multi-master mode.  It was apparently adequate for their needs, but I
> > > don't know what happens if/when one of the db machines fails.  I've
> > > heard that multi-master database replication is a thorny problem from
> > > a theoretical perspective (I think it was Seneca and Christopher
> > > Browne I overheard at a LUG meeting).  I also remember that the tech
> > > support guru occasionally had to issue strange commands to get things
> > > unwedged that included a memorized magic byte offset into MySQL's
> > > binary logs.  On the other hand, this company had 24x7 uptime
> > > obligations to its customers and unscheduled downtime had direct
> > > consequences on their bottom line, so the replication must have been
> > > doing something worthwhile.
> > >
> > > I prefer PostgreSQL for my own database needs, but I think it's
> > > because I was exposed to PostgreSQL before MySQL, and, at the time,
> > > MySQL's position on ACID was reprehensible.  I hear that MySQL 5 is
> > > much better ACID-wise, and it's had replication for a long time.  It
> > > might be worth looking into.
> > >
> > > Ian
> > 
> > Well, I use roundcube webmail with MySQL holding it's data (couldn't get
> > it working on PgSQL). Otherwise I wouldn't have to worry about MySQL at
> > all. In this case though, I do, so thank you for the info. I hadn't
> > asked about MySQL yet because I was trying to keep my poor noggin'
> > focused on as few crazy things as possible. In our case though,
> > switching to MySQL is both not appealing and not practical. It's nice to
> > know it'll work for the few instances we need it though!
> > 
> > Madi
> > 
> > 
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