2. Writing Tapes
 | The stageareas on the DAQ systems are not backed up by the computer group. The home directories are periodically saved to another system in case of catastrophic failure. The safety and security of your data is your responsibility |
This section describes how to write the data in your event and home directories to tape. Normally these are written as two separate tape sets. You must write these tapes on either daqtape1.nscl.msu.edu or daqtape2.nscl.msu.edu These are systems with tapedrives located in the rack to the right of Data-U 2. It is very important to match the correct media with the correct drive type, as well as to ensure that the media you use can be read on the drives available either at your home institution, or the systems at the NSCL where you intend to read these tapes.
These systems have the following drives attached to them:
Table 1. Tape Drives available on daqtape1.nscl.msu.edu
| Tape Drive | Drive Type | Capacity | Media |
|---|---|---|---|
| /dev/st0 | LTO-1 | 100 Gbytes | LTO-1 |
| /dev/st1 | DLT IV | 10 - 50 Gbytes | DLT IV |
Table 2. Tape Drives available on daqtape2.nscl.msu.edu
| Tape Drive | Drive Type | Capacity | Media |
|---|---|---|---|
| /dev/st0 | LTO-2 | 200 Gbytes | LTO-2 |
| /dev/st1 | DLT IV | 10 - 50 Gbytes | DLT IV |
The procedure described below can also be used to backup your data while you are running your experiment.
2.1. Writing event data to tape
| Do these steps on daqtape1.nscl.msu.edu or daqtape2.nscl.msu.edu (depending on your space requirements). |
Event data is all symbolically linked to the experiment subdirectory in the user home directory. Each run has a subdirectory with a link to the event data for that run in the subdirectory. The actual location of the event data, is in the user's stagearea at ~/stagearea/complete.
We recently have been made aware of at least one incorrect experiment apparatus setup script that creates a circular link in the ~/experiment directory. If you follow the procedure described below with the circular link in place, the circular link will cause the backup of the stage area to continue indefinitely.
To see if you have this circular link, issue the following commands:
bash$ cd ~/experiment
bash$ ls -l experiment
If this gives output like the following:
lrwxrwxrwx 1 fox manager 20 Nov 28 08:43 experiment -> /user/fox/experiment
(substituting your experiment account name for "fox" in the output above),
you should remove this link as follows:
bash$ rm experiment
How you write the experiment data to tape depends on which version of NSCDAQ's readout GUI you are using, as data files were reorganized recently. If ~/experiment is a directory:
bash$ cd ~/experiment
bash$ tar -chMf tapedrive . --exclude=.zfs
If, on the other hand, ~/experiment is a symbolic link to an experiment
directory in the stagearea:
bash$ cd ~/stagearea
bash$ tar -cMf tapedrive . --exclude=.zfs
Where:
tapedrive is the name of the tape drive to which you are writing data
The tar command switches are documented in the the tar(1) manpage, however the key points are that the "M" switch allows the tar set to span multiple tapes and the "h" switch copies the files that symbolic links point to (their contents), rather than copying the links themselves.
Once you have written this tape, it is a good idea to create a file containing a listing of the tape contents. You can examine this file to verify that the files you expect to find on the tape are actually on the tape. To create this listing file, mount the first tape of the stage area backup in the drive and:
bash$ tar tMf tapedrive > listingfile
2.2. Writing home directories to tape
| Before backing up your home directories to tape be sure you have removed the last of your event area tapes from the drive and replace it with a blank tape. You should use separate tape sets to back up the event and home directory trees. |
To write the home directories to tape, excluding the event data and any links to it we recommend that you use the following command:
bash$ cd ~
bash$ tar -cMf tapedrive . \
--exclude=.zfs --exclude=./experiment --exclude=./stagearea
Where:
tapedrive is the name of the tape drive you want the data written to.
the --exclude=experiment and --exclude=stagearea switches ensure that you don't write the event data again
We have omitted the "h" switch in case there are links to the event data areas
It is advisable to create a listing of the contents of the home directory backup tape(s) as well. See the previous section for instrutions that describe how to do this.
| This procedure assumes that you have not manually put any data into the event stagearea. That is the only data in the stagearea is that put in there by the NSCL DAQ software |