Performance Mainframe vs PC (clustering, grid computing)
Category: Computers > Hardware
Asked by: jkrech17-ga
List Price: $5.00
28 Sep 2002 11:08 PDT
Expires: 02 Oct 2002 18:12 PDT
Question ID: 70183
I am trying to write a paper on mainframes vs pc's and I am to the point of performance. I am trying to illustrate that today's pc's with technolgies like distributed/grid computing, and clustering can outperform a mainframe and essentially eliminate the I/O difference between the two platforms. Can someone lead to to a site with some comparisons or statistics? Thanks a lot for your help in advance. I have included what I have so far below: Performance would probably have been the biggest difference between the mainframe and todays PCs; however, with processor speeds climbing and new technology such as clustering and grid computing, PCs will put up a good fight. The only big difference I can determine is the I/O capability between the two platforms. From researching mainframes, it seems as though they have a lot of redundancy and serviceability features built in that allow them to handle I/O much more efficiently than a lower end PC. A mainframe can handle a large amount of simultaneous I/Os and has the ability to page them quickly. The following chart will illustrate the I/O capability of a mainframe class machine, just between different sun machines. The Sun Fire 15k can have up to 72 I/O slots with a combined bandwidth of 21.6 GB/sec (www.sun.com/servers)! Product Specifications Sun Fire 3800 Sun Fire 4800 Sun Fire 4810 Sun Fire 6800 Sun Fire 12K Sun Fire 15K CPUs 2-8 2-12 2-12 2-24 4-52 4-106 Processor UltraSPARC III Cu UltraSPARC III Cu Clock speed 750-MHz, 900-MHz or 1.05-GHz 900-MHz or 1.05-GHz Uniboard CPU/Memory Boards 2 3 3 6 Up to 9 Up to 18 I/O Slots (cPCI/PCI) 12 cPCI 16 PCI or 8 hot-swappable cPCI 32 PCI or 16 hot-swappable cPCI 36 PCI hot-swappable 72 PCI hot-swappable I/O Bandwidth 2.4 GB per second per PCI/cPCI assembly 10.8 GB/sec 21.6 GB/sec Those are pretty amazing figures especially when an Intel Xeon platform PC can provide a maximum of 3.2 GB/sec (www.intel.com).
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Re: Performance Mainframe vs PC (clustering, grid computing)
From: aceresearcher-ga on 29 Sep 2002 10:49 PDT
Having worked in the IT department at a large bank and at a Top 10 investment firm, I can tell you this: The reason mainframes still exist at many large companies is because PC technology is not currently (and may never be) able to do the kind of transaction processing required by these firms. Most firms of this type run a nightly batch cycle to "apply" the day's (thousands or even millions of) transactions to their huge database. They do this because this is still the best way to process this kind of transaction volume in the timeframe available, and to maintain such large databases (databasii?) The statement you made about mainframes' superior I/O handling is generally true. While most firms with such extremely large processing requirements, now that Y2k (Year 2000 bug remediation) is a thing of the past, are converting to or adding on a PC-based "front-end" system that supports on-line banking using PCs, their "back-end" system is still a mainframe that supplies the sheer "transaction crunching" power required. Bear in mind that, since customers tend to be very touchy about things like money, in the event of a power failure or catastrophic hardware or software failure, these businesses need to be 1) absolutely sure that they will not lose any data from previously processed transactions and 2) able to get up and running again immediately (or as soon as possible). Hence the need for double- and even triple-redundant systems, and the need to write each transaction 2 or 3 times (high I/O) to support that redundancy. Consequently, any cost-benefit and performance analysis of mainframes vs. PCs is dependent on the volume and the timeframe of the required processes. You will not be able to write a paper showing that PCs can ALWAYS provide the same performance for a lesser cost. However, you should be able to make a case that for many businesses, PCs would be able to provide the performance required at a substantial savings (remember that the businesses' potential growth factor must also be considered). While the information you get would obviously be slanted to the company's benefit, companies such as IBM, HP, and Sun would probably be able to provide you with some of the promotional information they have already developed to persuade potential clients that their system is the best solution. You might try contacting the sales departments of these companies, explain what you are looking for, and see if they are willing to provide with such information on- or off-line. Hope this information is of some assistance. Good luck!
Re: Performance Mainframe vs PC (clustering, grid computing)
From: maniac-ga on 30 Sep 2002 18:49 PDT
Hello jkrech17, I can provide a counter example (and won't post as an answer unless you want it) that shows that the application may require significant changes when moving from a large computer (or mainframe) to a cluster of smaller ones. This is a real example - taken from a system I am working on to move from an SGI Challenge XL to a cluster of PC's connected by Scalable Coherent Interface (operating similar to shared memory). The Everest bus on the XL (several years ago) provides several gigabytes per second transfer rate between CPU cards, memory, and I/O cards. Accesses to memory are cache coherent - a write by one CPU to memory will update caches for all other CPU's as necessary. A new Origin machine was priced at about $500k. Go to http://www.sgi.com/ for more information. The SGI machines are not typically called mainframes, but these machines happen to share some of the characteristics of a mainframe. SCI has 1 Gbyte/second connections, but data transfers are usually restricted to 100 Mbyte/sec on 33 Mhz/32 bit PCI (or up to 200-400 Mbyte/sec on 64 bit PCI). Latency for a memory access on another node is usually 2.5 microseconds, but caching will improve performance to bus rates on reads / writes to consecutive addresses. Caches across the cluster are not coherent, and the order of writes are not guaranteed unless cache flushes are used to sequence writes. The cluster with a lot more CPU power and memory runs about $80k. Go to http://www.dolphinics.com/ for information about SCI, and references to vendors that will sell SCI clusters. The application generally works except for... - congestion can occur on a bus to delay SCI transfers to over 256 microseconds (measured). This cause problems on a VME bus where an 80 microsecond time out was programmed into the bus controller. - the lack of write ordering and cache coherency adds complexity to code that must use cluster shared memory. Do not under estimate this latter effect, search with phrases such as "cache coherency", "weak memory model", or "write ordering" for articles that describe this. To give you an idea of the impact of this, transfer of 64 bytes in a message takes about 9 microseconds to move the data and 40 microseconds to get a lock, update pointers, and release the lock. There is also a lot more code required to do this properly. Don't get me wrong, we are happy with the new hardware - especially the cost of maintenance and performance of each system in the cluster, but the software costs and latent bugs due to a brittle design have pretty much eaten up the benefits. --Maniac
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