Some Frequently Asked Questions about DAQ

• Q: Where is the data ? Use a command ``find_run 1745'' to find where run 1745 has been written on disk and MSS. The data are first written to disk. Files are automatically split, with suffixes .0,.1,.2...etc. Splitting occurs at 2 Gbytes to avoid problem of system file size limit. Files are archived automatically to tape in the MSS tape silo. Two tape copies are made. Data are purged from disk automatically. Users should never attempt to copy, move, or erase data.

• Q: How to adjust prescale factors ? Edit the file /home/adev/prescale/ prescale.dat. One common problem is putting typographical errors here which then leads to no triggers getting accepted.

• Q: What is the deadtime ? The deadtime is displayed in the datamon window, which normally is running next to the runcontrol window, but if this window is not up, type ``datamon'' to bring it up. This window also shows the full-path-name of the file being written by CODA for the present run.

• Q: Why is the deadtime so high ? (and related) Search for answers among the following. The standard lore is that 30% deadtime is tolerable, but you should ask your analysis team to decide. Sometimes people seeing large deadtimes have forgotten to observe that the beam is in pulsed mode. Another possibility is that the workstation is overloaded. The computer used for CODA should not be used for much else. Do not attempt to read or write rapidly to the same physical disk to which CODA is writing. Sometimes it is observed that the workstation itself is very sluggish. This could be due to a foreign mounted disk having gone away, and there are other possible reasons. If a Cold Start of CODA doesn't solve this, you may try rebooting the workstation (see computer section). Also, if the event size changes substantially, e.g. due to noise conditions, the deadtime as a function of rate will change, especially in the regime of high rates.