Arthur Kreymer - 25 April 1995

E831 Express Analysis

E831 Express Characteristics:

E831 Express Requirements

In the 1990/91 E687 run, the ability to analyze small samples of data quickly in the counting room played a major role in our ability to keep the quality of the data high. We also derived some advantage from the "expressline" Silicon Graphics system in the Feynman Center, used to run the occasional full data tape to theck charm signals, and used to reconstruct some special calibration runs shortly after they were taken.

For the E831 data run we plan to have a much more powerful Express Analysis system in the counting room. Based on the projected budget and typical systems presently available, we can expect at least 500 SPEC of CPU power. The system should be configured with appropriate disk and tape, for staging of data and logging of results.

We plan a data taking rate of about 20,000 events per spill, at about 5 KBytes per event. This implies a sustained data rate of about 1.6 MBytes/second and 333 events/second. The full analysis of an average E687 event requires about 20 SPEC-seconds. Thus, if everything remained the same for E831, a 500 SPEC farm could analyze 7% of the data. ( Event sizes may increase due to the new Vertex and Straw detectors, and analysis time could increase somewhat. )

While this fraction of the data corresponds roughly to a full analysis of E687, and would provide good online charm signals and powerful diagnostics, there may be even better stategies for use of the Express system. We would like to get a larger fraction of the charm signal for monitoring, and for early access to Physics signals.

The full analysis of E831 events will be slower than for E687, due to the additional detectors and improved efficiencies. But full calorimeter reconstruction will probably not be available, nor will it be necessary for most of the Express monitoring. Streamlined calorimitry would probably bring the Express reconstruction down to half the time of full E687 reconstruction, allowing 15% of the events to be analyzed.

We can make physics based event selections, through Online and Offline methods. A combination of online and offline selections could be used. If we are clever, we could see a large fraction of the final charm signal in some modes. The Express system should write output tapes, mostly in DST format to keep down the tape and data handling costs. We will write no more than 1/10 as many tapes as the full data stream.

Offline selection
With all events available, a rapid partial analysis could select events for complete analysis. Selections could include a combination of:
Online selection
Trigger bits from Level II may provide more Et, muon, and other information than we use to select events for logging. These trigger bits could be used in Expess event selection.

Implementation

We will discuss here the analysis model, data links, farm configurations and peripherals. Some reference systems will be described, based on vendor's catalogues. These descriptions are not necessarily complete or correct, and other considerations may lead us to alternate systems.

Let us assume, for reference, that we are working with a $150,000 total budget. Based on Farm experience it is reasonable to plan on substantial peripheral support, so that the available CPU can be used efficently. Let us assume a budget of

Analysis Model
Input data files will be stored on disk in the Express system. The slowest individual CPU's we should consider are 100+ SPEC's, comparable to the 300 SPEC power of a typical farmlet used in the E687 analysis. We should not need formal farm managent systems like CVS, PVM or SHIFT. Each input file can be analyzed by a single process. We can afford to store several tapes of input and output data on disk, decoupling Express processing from media handling.
Data Link
Reading data into the Expresss system from tape would be expensive in terms of labor, drive maintenance, and risk to the tapes. Available network links permit the data to be obtained directly from the Logger. It appears that several good options are available. We may need to add memory to the Logger to provide adequate decoupling of the Express and Logging functions and to reduce Logger bus activity.

Some network options:

Farm Configurations
Multiple CPU's are required in order to obtained the required total computing power. CPU's may be configured with Shared Memory on a shared high speed bus (SMP), or may be purchased as standalone workstations in a Farm. On an SMP system we will simply start one analysis task per CPU, and let the system take care of scheduling and communication. On a Farm system, a Host node will NFS serve the data disks. We will run one analysis task on each Worker node. A fast network hub connects to the Host via FDDI or Fast Ethernet, connects to the Workers via regular ethernet, and buffers the farm from the general E831 network.
Peripherals
We plan to produce only about 200 KBytes/second of output. A single EXB-8505 will suffice for output logging. A second drive is required for backups, and for a hot spare. Three more drives, for a total of 5, will allow us to perform reanalysis during beam down periods. The five drives should cost about $10K.

The highest data rates are on the disks holding the input data files. To avoid head contention, we must try to analyze from one disk while filling another. If analysis keeps well ahead of the data source, this requires two input disks. It is quite likely that we will tune analysis to keep only slightly ahead of the data. Therefore we need three input data disks. Output data rates are low, but head contention can still prevent tape streaming. Therefore we should plan on two output data disks. Five data disks, at about $3K per 9 Gb, would cost about $15K

We should plan on at lest $5K for cables, chassis, etc for the peripherals.

Reference Systems
For the remaining $120K, we list some reaonably cost-effective systems, presently orderable from each of the Fermilab supported vendors. We may not have a free choice of vendors, and the information listed here may be incomplete.

Both small-node Farm and SMP systems are listed when available. Published retail prices for standard configurations are used. I have omitted Fermilab discounts, as well as software, maintenance, networking and other infrastructure costs. These factors may roughly cancel out, but the Devil is in the Details. The numbers listed below should be used only to get a rough idea of how well we might do. Systems are listed in inverse alphabetical order.