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Charles Curran IT/PDP
Visitors to the Computer Centre will have noticed that the existing Storage Tek tape library has recently been extended. It is now configured as 4 Powderhorn 9310 silos, each capable of holding approximately 6,000 cartridges. All are interconnected.
The most recently added silo is equipped with 10 of STK's newest tape drive, the 9840. This unit is considerably cheaper than the Redwoods already installed, but offers a much higher performance than what are sometimes called 'commodity' tape units (in which category we include the DLT 2000 unit, for example).
Read and write speed is 10 MBytes/sec, and the cartridge used by
the unit can hold up to 20 GBytes of data. These are the native
speed and native capacity, which ignore any effects of the data
compression which the unit also offers. Recording is linear
serpentine, not helical, over 288 tracks. See STK's web pages at
URL:
http://www.storagetek.com/StorageTek/hardware/tape/9840/
for details.
See CERN's web pages at URL:
http://wwwinfo.cern.ch/pdp/vm/picture/stk9840.gif
for a view of CERN's 9840s.
...which use new media.....
While these are already quite impressive performances, the 9840
has another novel feature. The cartridge or cassette
('cassette' describes its design more clearly) contains tape which
is wound onto two reels contained within the '3480' form factor. It
thus requires no complicated threading into the unit. The cassette,
once presented to the unit by the Powderhorn robotics, is loaded
and initialised ready for operation in only 4 seconds, and can seek
to any data on the tape in a little as 8 seconds. This is much
faster than either the STK Redwood or the IBM 3590, and makes this
media and unit particularly suited to accessing relatively
scattered files on one or more cassettes rapidly. There are 300
such cassettes in the library, which carry pre-printed stickers
(R01001-R01300, with media identifier 'R'). See CERN's web pages at
URLs:
http://wwwinfo.cern.ch/pdp/vm/picture/9840cart1.gif
and
http://wwwinfo.cern.ch/pdp/vm/picture/9840cart2.gif for views
of a 9840 cassette.
The characteristics noted above may well be quite attractive to many users, but the cassette itself is more expensive per GByte than the Redwood, so we do not expect it to be used for an application such as bulk recording of raw experimental data. However, there are some cartridges at CERN that are accessed very often, which are used rather regularly in 'append' mode for journalling or in 'append' mode for some relatively low-volume Central Data Recording applications.
We anticipate that its characteristics will allow us greater flexibility in our storage system plans, offering a device that is cheaper than disk, but much faster in providing access to data than any of our existing tape units. Systems such as HPSS can exploit devices of different characteristics without explicit user intervention rather easily by using an appropriate 'Class of Service'; improvements to the current SHIFT software will probably do the same. It should also be simpler to offer a service which users see as 'high reliability' with such a unit: considerable effort is still required to provide such a service with Redwoods.
We will try to contact users with appropriate usage patterns to
see if they would like to use this new offering. Equally, if you
are interested, you can send an e-mail to
Tape.Support@cern.ch, and we will be happy to discuss
what use you might wish to make of the 9840.
For matters related to this article please contact the author.
