HP (Tandem) Non stop 与 Linux 集群相比如何？
HP NonStop 系统（以前称为“Tandem”）以其高可用性和可靠性以及较高的价格而闻名。
在这些方面和其他方面，基于 Linux 或 Unix 的集群与它们相比如何？
HP NonStop systems (previously known as "Tandem") are known for their high availability and reliability, and higher price.
How do Linux or Unix based clusters compare with them, in these respects and others?
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在容错机器上，容错直接在硬件中处理，并且对应用程序透明。 对集群进行编程需要您显式处理应用程序中的容错能力。
实际上，与为容错平台（例如 NonStop）构建的应用程序相比，集群应用程序架构的构建要复杂得多，并且更容易出错。 这意味着应用程序错误导致的不可靠性范围更大，如伦敦证券交易所 经过一番艰难的探索才发现。他们有一个现有的基于 Tandem 的系统，这是证券交易所交易应用程序的一种常见架构。 他们的新任首席执行官有一个聪明的想法，即微软是前进的方向，并让一家 5 强咨询公司构建了一个基于 120 台服务器集群的 .Net 系统。
集群应用程序的问题在于故障可以相互关联。 如果系统中存在应用程序或配置错误，它通常会复制到所有节点上。 这意味着您可以获得可以摧毁整个集群的单一情况或事件。 集群应用程序的额外复杂性使它们在开发和部署时更容易出错，从而增加了发生这种情况的可能性。 例如，基于 Linux 和 J2EE 构建的集群系统很容易受到相同类型的故障模式的影响。
恕我直言，这是旧式大型机架构的主要优势。 有几个供应商（IBM、HP、DEC 以及可能还有其他几个我想不到的供应商）制作了容错系统。 此类系统的底层编程模型比集群式 n 层应用程序服务器稍微简单一些。 这意味着出错的可能性相对较小，并且通过一定的努力，您可以实现更可靠的系统。 令人惊讶的是，数量惊人的旧建筑仍然存在，而且运行良好，并且在其市场利基市场中生活得相当舒适。 IBM 仍然销售大量 Z 和 I 系列机器； Unisys 仍然生产 A 系列和 2200 系列； VMS 和 NonStop 在 HP 中仍然存在。 这些系统的销售并不全部面向现有客户 - 例如，商业承保系统 (GENIUS) 在 ISeries 上运行，并且在我撰写本文时仍然是该领域的市场领导者，新的推出正在进行中。 据我所知，该应用程序已经经历了两次重写尝试（一次在 Java 中，一次在 .Net 中），并且“老派”平台似乎并没有真正限制其风格。
我还不会做空任何屏幕抓取供应商
...... Reuter 的事务处理：概念和技术有些枯燥和学术性，但有一个良好的容错系统架构处理。 其中一位作者是 Tandem 系统设计的关键参与者。
On a fault-tolerant machine the fault tolerance is handled directly in hardware and transparent to the application. Programming a cluster requires you to explicitly handle the fault tolerance in the application.
In practice, a clustered application architecture is much more complex to build and error prone than an application built for a fault-tolerant platform such as NonStop. This means that there is a far greater scope for unreliability driven by application bugs, as the London Stock Exchange found out the hard way. They had an incumbent Tandem-based system, which was quite a common architecture for stock exchange trading applications. Their new CEO had the bright idea that Microsoft was the way forward and had a big-5 consultancy build a .Net system based on a cluster of 120 servers.
The problem with clustered applications is that the failures can be correlated. If an application or configuration bug exists in the system it will typically be replicated on all of the nodes. This means that you can get a single situation or event that can take out the whole cluster. The additional complexity of clustered applications makes them more error-prone to develop and deploy, which raises the odds of this happening. A clustered system built on (for example) Linux and J2EE is vulnerable to the same types of failure modes.
IMHO this is a major advantage of older-style mainframe architectures. Several vendors (IBM, HP, DEC and probably several others I can't think of) made fault tolerant systems. The underlying programming model for this type of system is somewhat simpler than a clustered n-tier application server. This means that there is comparatively little to go wrong and for a given amount of effort you can achieve a more reliable system. A surprising number of older architectures are still alive and well and living quite comfortably in their market niches. IBM still sell plenty of Z and I series machines; Unisys still makes the A Series and 2200 series; VMS and NonStop are still alive within HP. The sales of these systems are not all to existing clients - for example a Commercial Underwriting system (GENIUS) runs on the ISeries and is still a market leader in this niche with new rollouts going on as I write this. The application has survived two attempts to rewrite it (1 in in Java and 1 in .Net) that I am aware of and the 'Old School' platform doesn't really seem to be cramping its style.
I wouldn't go shorting any screen-scraper vendors just yet ...
Gray & Reuter's Transaction Processing: Concepts and Techniques is somewhat dry and academic, but has a good treatment of fault-tolerant systems architecture. One of the authors was a key player in the design of Tandem's systems.