We are planning to make some changes in the peripherals attached to the data-taking Suns at KPNO. Before the start of the fall observing semester, we hope to supplement the Exabyte 8200 8-mm tape drives in the domes with Exabyte Eliant 820 drives. Eventually (but not for at least a year), the Exabyte 8200 drives will be removed. We also plan to remove all the HP 35480 DDS-1 DAT (4-mm) tape drives and replace them with Seagate Scorpion-8 DDS-2 drives.
These new drives are cheaper, faster, more reliable, more flexible and hold more data on a cartridge than the drives being replaced. However, you now have to make some important choices when you write your data to tape. Both the type of tape you use and the "density" you specify are important. Make sure you know what the capabilities of your tape drives at home before you make your choice! For example, tapes written on one of the new Exabyte Eliant 820 drives cannot be read on an older Exabyte 8200 drive.
The existing Exabyte 8200 drives write in "low density" on 112-m tape cartridges (nominal capacity: 2.5 GB). The new Eliant 820 drives can write in "high density" on 112-m tape cartridges (nominal capacity: 5.0 GB) and "high density" on 160-m tapes (7.0 GB). The DDS-2 DAT drives can write on 60-m tape cartridges (nominal capacity: 1.3 GB), 90-m tapes (2 GB) and 120-m tapes (4 GB). IRAF provides device names for all these possibilities: please check the lists posted in the domes or the "devices" command within IRAF for details.
Note that once we retire the Exabyte 8200 drives from the domes, observers will no longer be able to conveniently make "low density" Exabyte tapes. However, we will endeavor to keep an 8200 drive operational as long as possible on our "media conversion" Sun located in the Administration Building.
The mountain office in the Administration building will stock 112-m and 160-m Exabyte tapes and 60-m, 90-m and 120-m DAT tapes for purchase. Remember, if you bring your own tapes, bring only computer grade (certified for Digital Data Storage) tapes.
Note that although both the Exabyte and DAT drives feature hardware data compression, we don't support the use of hardware compression through the IRAF device names. We have found that hardware data compression is not very effective on CCD frames. Furthermore, when hardware data compression is used, the length of tape occupied by each file cannot be determined thus invalidating the use of IRAF's "tapemon" task to monitor the amount of tape used. However, there is a move afoot to provide in the future a facility within IRAF to more intelligently compress data before it is written to tape.
We have had some terrible reliability problems with our DAT tape drives over the past year which has led to our decision to replace all of our existing HP 35480 DAT drives. During testing of the new Seagate DDS-2 drives, we have discovered that our old HP 35480 DDS-1 drives can not read successfully tapes written with the new DDS-2 drives. All other DAT drives we tested read the tapes fine. This result has shaken our faith in DAT drive interoperability (and reinforced our decision to throw away the HP 35480 drives!). We advise checking carefully that your DAT drives at home can read DAT tapes written with our drives before committing valuable data solely to DAT tapes. Towards this end, we are willing to send you a DAT tape written with our new mountain DAT drives: contact observing support.
Finally, note that nine-track tape drives are no longer installed on any of the dome data-taking Suns at KPNO. There is one nine-track drive installed on a Sun in the Administration building (also featuring Exabyte and DAT drives) which may be used for post-observing data conversion.
Steve Grandi (grandi@noao.edu)
Rob Seaman (seaman@noao.edu)