4mm Tape vs. TR-4 vs. DLT
Phil Wong
I am debating which type of tape drives to purchase to backup a network of
Macs and PCs.
Which tape backup media stands out from the rest ?
4mm ? TR-4 ? or DLT ??
Why should you buy one and not the others ??
BTW, How come DLT drives are so outrageously expensive ?
Any insights will be appreciated.
Richard Tomkins
I'm going to take a stab at this, but it sometimes becomes a religous thing.
FWIW, I work for DIGITAL, er, COMPAQ, and we invented DIGITAL Linear Tape
and then sold the technology to Quantum.
In article <philwong-300...@user-38ld1r2.dialup.mindspring.com>,
phil...@mindspring.com (Phil Wong) wrote:
> I am debating which type of tape drives to purchase to backup a network of
> Macs and PCs.
>
> Which tape backup media stands out from the rest ?
Digital Linear Tape stand out from the rest. It has the fastest MegaByte
per minute transfer rate. As the tape passes the heads in a linear
fashion, rather than being wrapped around a rotating head, it has a faster
search/rewind speed. Linear Tape is naturally a Streaming Tape, thus keep
up the data rate, and the tape runs non-stop. If you have start stop,
Linear tape has faster acceleration for both starting and stopping and
this outperforms DAT, as the DAT must do a lot of re-positioning and
Start/Stop is not it's forte.
>
> 4mm ? TR-4 ? or DLT ??
>
> Why should you buy one and not the others ??
Digital Linear Tape made by Quantum or Digital has a multi-pass life
expectancy that is in excess of 10,000 re-writes, that is, if you
purchased DLT today, and you did backups in a grandfather, father, son
manner, so the same tape get's used every third week, the tape will
outlive you by more than 50 years.
>
>
> BTW, How come DLT drives are so outrageously expensive ?
The mechanism is precision machined and assembled. It is not made from
light tin metals like many DAT drives, it has a solid machined cast metal
base and the guides that control tape path alignment are all ball bearing
mounted, etc...
If you want to know, the airforce uses DLT to record flight data on
Fighter Aircraft, and a DAT tape would fail, but a DLT takes the high G's
and keeps on going.
The compression algorythm is proprietary, designed to compliment the DLT
design and media capabilities rather than being generic.
All tapes are self calibrated upon first insertaion into a drive, thus
ensuring that all other DLT mechanisms can calibrate to the tape and
successfully read or write.
rtt
hei...@ecs.umass.edu
In Article <philwong-300...@user-38ld1r2.dialup.mindspring.com>
phil...@mindspring.com (Phil Wong) writes:
>I am debating which type of tape drives to purchase to backup a network of
>Macs and PCs.
>
>Which tape backup media stands out from the rest ?
>
If the amount of money is not an issue, then of the three DLT is the
best without a question. A new technology of tape drive that has
capacity and speed approaching DLT is AIT. AIT also costs a similar
amount as DLT. Long term experience is needed with AIT to see if it
will surpass DLT, be just an alternative to it, or be the next choice
after DLT if you do not need some aspect of DLT that is better than
AIT.
>Why should you buy one and not the others ??
It all comes down to which drive will meet your set of needs when you
take price, amount of data and frequency you need to backup, as well
as issues of reliability and ease of use into consideration. Here
are some pros and cons for the three you ask about plus AIT. The 4
drives actually can be considered as falling into two categories, the
low end and high end of backup tape drives.
4mm - Pros are lower tape costs, higher available capacity than TR-4
when you use DDS-3 tapes and drives. DDS-2 drives with an 120m
tape is the same capacity as TR-4 - 4 GB native/8 GB compressed.
Cons - drives are more expensive, mechanisms are more delicate/
mechanically complicated - DAT drive internally is like a size
reduced VHS recorder. DAT tapes can take fewer recording/reading
passes, and finally except for the fastest/most expensive DDS-3
drives the transfer rate is a bit slower than TR-4.
TR-4 - Pros - Simpler/more rugged mechanism, tapes will take many more
passes than DAT, slightly higher transfer rate for data, lower
cost for the drives, wider tape is less subject to damage. New
TR-5 drives up the capacity to 10 GB/20 GB, native/compressed.
Cons - tapes more expensive than DAT, drives a bit noisier than
DAT, cartridges physically larger than DAT.
DLT - Pros - Highest transfer rate of the four, mechanisms designed
for heavy duty use, highest capacity - current DLT70 drives can
store 35 GB/70 GB compressed per tape, with 7 tape autoloader
available can be setup for unattended backup of hundreds of GBs
of files, tapes are rated for many, many times a number of passes
as DAT and AIT. May be only practical method of backing up large
networks of machines.
Cons - High cost for drives and tapes, needs fast computer and
SCSI connection to get its maximum data throughput.
AIT - Pros - Transfer rate nearly as fast as DLT, high capacity tapes -
25 GB/ 50 GB with compression.
Cons - same as for DLT, personal con against drive is short length
of time AIT drives have been in service - long term reliability is
not yet known.
>BTW, How come DLT drives are so outrageously expensive ?
Mostly because they are not designed to low end consumer quality standards
you may be used to seeing drive prices in the Mac and PC equipment market-
place. They were designed to meet the needs of mid to high end computer
workstations and medium to large networks of computers and data storage.
The DLT mechanisms are designed so they can be used 10 hours a day or more
and used every day of the year. It takes quality components made to tight
tolerances to move data at rates over 100 MB/minute reliably onto 1/2"
tape written in one of over a hundred tracks done one at a time the length
of the tape. And partly they are as expensive as they are because they
find buyers at that price, mostly because the alternatives to backup as
much data at the same or higher speeds are even more expensive. DLT prices
have been coming down though as later models are introduced, same as for
any other equipment.
>Any insights will be appreciated.
Hope this helps. I would also point you torwards APS Technologies web
site, www.apstech.com. They have a table that lists the various backup
tape drives and list some of the specs for transfer rates, tape life and
other other items that you may find useful if you need some quantitative
comparisons instead of the qualitative ones I have given here.
Joe Heimann
hei...@ecs.umass.edu College of Engineering
Engineering Computer Services University of Massachusetts /Amherst
Richard Tomkins
I forgot to mention Autoloaders. DLT AutoLoader mechanisms come in many sizes.
I was stroking a 4 drive Digital unit the other day that could handle 48 tapes.
You can get even larger libraries if you need them.
rtt