Writing Data to Tape


Topics Covered:

  • Types and Locations of Tape Drive
  • 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 Problesm
  • Backing Up Your Data After Processing
  • Dirty Tape Drives
  • Tape Lifetimes


  • Types and Locations of Tape Drive
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    MACHINE DAT EXABYTE DLT
    RGLINUX4 no no yes
    RGLINUX5 no no no
    RGLINUX6 no yes no
    RGLINUX7 yes no no
    RGLINUX8 yes no no
    RGLINUX9 yes no no

    Notes:
    1. RGLINUX4 has the only available DLT drive, but is no longer available to the public. Please let one of us know, if you would like to use this backup medium.
    2. There are no tape drives on RTDC1-4. Please remote mount, if you are running AIPS on one of these machines. All drives are in M342.


  • Mounting, Reading from (or Writing to), and Dismounting Tapes within AIPS
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    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 (AIPS and tape drive on the same machine),
        intape = 1.
      • If you are mounting remotely, intape = 2 (or 3).
    3. Set the value of density in MOUNT or on the physical tape drive. Appropriate values are given in the table below.

      4. TAPE TYPE DENSITY IN MOUNT DENSITY ON DRIVE
      EXABYTE (54m) 6250 N/A
      EXABYTE (112m) 22500 N/A
      EXABYTE (160m) 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 (=1), if you are reading from (or writing to) a remote tape drive.
    6. Software mount your tape, i.e., type: MOUNT.
    Notes:
    1. An example of remote mounting: If you are running AIPS on RTDC2 and wish to mount a DAT on RGLINUX7, set intape = 2 (or 3); density = 6250; remhost = 'rglinux7'; remtape = 1
    2. We do not encourage writing to EXABYTE, since our single drive will not be replaced when it breaks.
    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.

  • Mounting, Reading from (or Writing to), and Dismounting Tapes at the unix Level
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    • Device names for reading from (or writing to) tape, e.g: with the tar command:

    MACHINE DAT EXABYTE DLT
    RGLINUX4 -- -- /dev/nst0
    RGLINUX5 -- -- --
    RGLINUX6 -- /dev/nst0 --
    RGLINUX7 /dev/nst0 -- --
    RGLINUX8 /dev/nst0 -- --
    RGLINUX9 /dev/nst0 -- --

    Notes:
    1. RGLINUX4 has the only available DLT drive, but is no longer available to the public. Please let one of us know if you'd like to use this backup medium.
    2. Tapes do not need to be mounted (or dismounted) when reading or writing at the unix level.


  • Common Tape Problems
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    1. Tape device left locked by someone else:

      2. 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 RGLINUX6 would be called: /aips/DA00/RGLINUX6/TAPE1.lock.

    2. Permissions problems and corrupted processes:

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

      1. /root/devnst (resets drive permissions)
      2. /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
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    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.

    TAPE TYPE CAPACITY (GB) DRIVE MODEL MACHINE
    DAT 72.0 DAT72 RGLINUX8
    DAT 40.0 DDS 4 RGLINUX7,9
    EXABYTE (112 m) 5.0 8505XL,8500 RGLINUX6
    EXABYTE (54 m) 2.4 8505XL,8500 RGLINUX6
    DLT 40.0 -- RGLINUX4

    Notes:
    1. RGLINUX4 is no longer available to the public, but the DLT drive can be used, if necessary.
    2. 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.
    3. See Muriel Hodges (M333 ext 6-7617) for DATs, EXABYTEs, or DLTs.

    Here is a detailed example on 'How to Back Up Your Data Files'

  • Dirty Tape Drives
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    A dirty tape drive may result in the following:
    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
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    Tape lifetimes depend critically on storage conditions. Temperature and humidity levels should be moderate and tapes should be exercised (read) at least once a year. Of course, there are exceptions. I (AA) have had a DLT (which is supposed to last more than a decade) become dysfunctional after a few months and an unexercised EXABYTE (with an expected lifetime of a few years) read perfectly after 12 years.


    		   
     
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