Topics Covered:

• Types and Locations of Tape Drives
• Mounting, Reading from (or writing to), and Dismounting Tapes within AIPS
• Mounting, Reading from (or writing to), and Dismounting Tapes at the unix Level
• Common Tape Problems
• Backing up your Data after Processing
• Dirty Tape Drives
• Tape Lifetimes

Types and Locations of Tape Drives

Mounting, Reading from (or writing to), and Dismounting Tapes within AIPS

To mount your tape:

1. Insert your tape into drive.
2. Set the value of intape in the AIPS verb MOUNT.
   • If you are mounting locally, EXABYTEs, DATs, and DLTs are assigned intapes 1,2, and 3, respectively.
   • If you are mounting remotely, intape must be set to 1 or 2 (RTDC1-3);  2 or 3 (RGLINUX6,8);  3 or 4 (RGLINUX5,7);  or 4 or 5 (RGLINUX4).
3. Set the value of density in MOUNT or on the physical tape drive. Appropriate values are given in the table below.

   TAPE TYPE DENSITY IN MOUNT   DENSITY ON DRIVE   EXABYTE (54 m) 6250 N/A EXABYTE (112 m) 22500 N/A   EXABYTE (160 m)   22500 N/A DAT 6250 N/A DLT leave at default (6250) 40.0

4. Set remhost, if you are reading from or writing to a remote tape drive.
5. Set remtape, if you are reading from or writing to a remote tape drive. EXABYTEs, DATs, and DLTs should be assigned the values 1,2, and 3, respectively.
6. Software mount your tape, i.e., type: MOUNT.

A few notes:

1. An example of remote mounting: If you are running AIPS on RTDC2 and wish to mount a DAT on RGLINUX7, set intape = 1 (or 2); density = 6250; remhost = 'rglinux7'; remtape = 2
2. We do not encourage writing to EXABYTE, since our two drives (one in use, one backup) will not be replaced when they break.
3. When setting the density on the DLT drive (left hand panel), make sure the compress light is off;  and when mounting, pull up bar on drive, insert tape in direction of arrow, and push bar back down.

To read (or write) the data from (to) tape:

Raw VLA, VLBA, and VLBI (correlated on a MkIII or MkIV correlator) data are read from tape using the AIPS tasks, FILLM, FITLD, and MK3IN, respectively. Previously processed AIPS data of any kind are read into AIPS using the task FITLD. Data that have been processed in AIPS are written to tape using the tasks FITTP or FITAB.

See the AIPS Cookbook for more details about these tasks.

To dismount your tape:

When you have finished with FILLM, FITLD, or MK3IN, issue the dismount command (within AIPS) and physically remove your tape.

Note: When dismounting a DLT, let it rest for a couple of seconds before pulling it out. The clasp that holds the tape doesn't always release immediately.

Mounting, Reading from (or writing to), and Dismounting Tapes at the unix Level

Tapes do not need to be mounted (or dismounted) when reading or writing at the unix level.

Device Names for reading from (or writing to) tape, e.g., with the tar command:

Common Tape Problems

1. Tape device left locked by someone else:

   Occasionally, someone will leave a tape mounted long after the AIPS task that used the tape has completed. If this happens, you can software dismount the tape as follows:

   Delete the file corresponding to the mounted device, i.e., a file of the form:
       /aips/DA00/[MACHINE-NAME]/TAPE[n].lock.
   For example, the file corresponding to an exabyte (tape device 1) mounted on RGLINUX5 would be called:
       /aips/DA00/RGLINUX5/TAPE1.lock.


2. Permissions problems and corrupted processes:

   Sometimes, one gets tape related error messages such as "permission denied" or "device busy" (even though there is no "TAPEn.lock" file). Two crons have been set up to deal with these problems:

   /root/devnst (resets drive permissions)
   /AIPS/tpmon (kills and restarts AIPS remote tape mount processes)
   The crons run once a day, at 6:00 AM. If there should be a problem between runs, "tpmon" can be executed by user "aips" and "devnst" by user "root".

   AIPS reads or writes that are executing at 6:00 AM will be compromised. Please plan accordingly.

Backing up your Data after Processing

Determine the size of your data files:

1. Run the AIPS task disku with sort='b' to see how large your data files are.
2. Convert blocks to GB, i.e., divide by 10⁶.
3. Multiply by 3 if filetype='uv'. Compressed (u,v) data expands by a factor of (approximately) three when written to tape; images do not.

Choose an appropriate backup medium.

1. Note the capacity of your backup medium and choose accordingly (see table below).
2. Set the "density" in the mount command as in step (3) of "Mounting and Dismounting your Tape."
3. Run the AIPS task fittp or fitab with appropriate inputs.

Notes:

1. The literature that accompanies DATs and DLTs often distinguishes between compressed and uncompressed data when talking about tape capacity. This is a hardware compression and is not the same as the compression of (u,v) data discussed above. AIPS can not do hardware compression, so if two numbers are given, one for compressed and one for uncompressed, choose the smaller.
2. See Muriel Hodges (M333) for DATs, EXABYTEs, or DLTs.

Click here for a detailed example.

Dirty Tape Drives

1. A parity error message (on computer screen) when reading from (or writing to) tape
2. A flashing orange light in DAT or EXABYTE drive after insertion of tape into drive
3. A message on DLT drive after insertion of tape into drive

Try cleaning the drive. Cleaning tapes are on the tables holding the computer monitors. Once inserted into the drive, the tape will run through its cycle and pop out on its own. Note that 160 m EXABYTEs are especially sensitive, so you'll probably want to clean the drive after every two or three uses.

Tape Lifetimes

Please note that large capacity media (e.g., DLTs and DDS 4 DATs) are more expensive than smaller capacity media (DDS 2 DATs). Use only as much storage as you need.