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Yeah, but let's be clear here: "rolling upgrades" means a completely redundant set of servers. You can't have, say, five servers and then one that backs up the other five. So the concept of redundancy on a server farm is no different than redundancy on an iSeries... except that with an iSeries you have many more options: 1. You can have a smaller backup box dedicated only to mission critical functions that is much cheaper than your primary box, and is used during outages. My guess is that maintaining such a system in a Windows environment is a bit more difficult. 2. You can have an offsite box that you lease from a DR firm for major outages. With creative planning, you can conceivably use this box for planned outages. I'd love to see the offsite DR system that can handle 20 Windows servers--or 120... and how much that costs. 3. You can partition your machine and use a small partition as the "backup" box as in option 1. This is less amenable to unplanned outages, but works very well for planned maintenance and can be a cheaper option (although with the price of a 500CPW machine down around $10K, it's harder for me to justify the cost and complexity of partitioning). POINT: A single machine is easier to maintain, upgrade, manage and failover than a cluster. A cluster provides no more failover capability than a single machine; you still need redundant machines, connections, etc. in order to successfully provide HA. Also, I don't know as much about Windows, Walden, but the vast majority of software upgrades for the iSeries can be loaded while the machine is running, and only a subset of them require so much as an IPL, which is indeed a wee-hours planned outage thing. Personally, I doubt there are a lot of truly 24/7 sites. Frankly, I see "system unavailable" messages on even supposedly 24/7 sites ("The electronic banking system is unavailable for planned maintenance") with far more regularity than I have ever seen an iSeries IPLed. POINT: iSeries upgrades are less frequent, less intrusive and require less overall downtime than Windows upgrades. Joe > From: Walden H. Leverich > > >Most importantly, business is 24x7. This application, once live, can > >probably withstand short downtimes in the wee hours each day, but not > >much more. > > Rich, > > Sure, the iSeries is stable, but it does go down. Sometimes (granted > rarely) in an unplanned way, but other times in a planned way, be it for > hardware upgrades, OS upgrades, full backups, PTF installs, etc. And > these planned downtimes are often more than "short downtimes in the wee > hours each day." > > So, if you need to be up nearly 24x7, are you planning on buying two > iSeries? > > Part of the advantage of a cluster is so the application can survive > "unplanned" outages, but the other advantage is the ability to do > rolling upgrades where you take a part of the cluster offline and > upgrade it, but the application continues to run on the other parts. > > Just something to add into the mix. > > -Walden
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