[comp.sys.hp] 8mm or DDS, which is better?

sgs@rand.mel.cocam.oz.au (Stuart Szabo) (06/18/91)

Does anyone know of what advantages 8mm has over DDS tape drives?
Or,  are DDS tape drives a better choice?   

Which has the better tranfer rates?

Which has better search algorithyms to locate files faster for extraction?

Which one is more of a standard?

Which has lower error rates?

etc, etc, etc, etc.

			Thanks,
				Stuart Szabo



-- 
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mark@hpcpbla.HP.COM (Mark Simms) (06/20/91)

Firstly, I work for HP on the development of DDS drives.  I will try
to be unbiased, but take what I say with that in mind.  Sometimes we
are the victims of our own hype.  These are my opinions.  They are not
those of HP.


>> Does anyone know of what advantages 8mm has over DDS tape drives?
>> Or,  are DDS tape drives a better choice?   

Which is better depends on many factors.  Both technologies have their
advantages.


>> Which has the better transfer rates?

8mm is noticeably faster.  The new 5Gbyte drives can transfer data
about 3 times faster than the current generation of DDS drives.  This
will probably remain the case for the foreseeable future since 8mm has
a head start.


>> Which has better search algorithyms to locate files faster for extraction?

DDS has far better search algorithms, provided your backup application
can use them.  DDS drives can find a given record or file mark on tape
in about 20 seconds on average.  The times can be several minutes for
a file mark and even longer for a record on 8mm.


>> Which one is more of a standard?

Depends what you mean by a standard.  DDS is an internationally
recognized standard accepted by various standards making bodies.  8mm
is not.  DDS is accepted as an interchange standard by several major
computer manufacturers.  8mm is not.  DDS is manufactured by several
companies.  8mm is manufactured by only one.  However, the installed
base of 8mm drives is larger than that of DDS drives.  DDS is catching
up, but what will happen in the long run is anybody's guess.


>> Which has lower error rates?

I don't know.  To be honest, I am not sure if anybody really does.  It
takes a lot of resources to do error rate testing, so independent
testing is very hard.  Both are probably "good enough".


>> etc, etc, etc, etc.

Capacity

I am sure you are aware that 8mm wins on capacity or you would have
asked the question.  However, just for completeness, 8mm drives are now
available that will store 5Gbytes on a single tape.  DDS drives can
store 2Gbytes on a single tape.


On drive data compression.

DDS drives have been announced that will use hardware data compression
to increase capacity and transfer rate.  If you have data that is very
regular and do not have the processor performance to compress data on
the host, then this may be of interest to you.


Form factor

DDS drives have been announced that are 3.5" form factor.  8mm drives
are 5.25" form factor.  If you require internal drives in desk top
systems then this might be important.


Reliability

Nobody really knows.  Like error rate testing, it takes a lot of
resources and there has been little independent testing.


In summary, I would say it depends.  If transfer rate during backup is
the critical issue, then 8mm is the best choice.  If host manufacturer
support is the issue, then buy whatever the host manufacturer
recommends.  If rapid restore is critical, then get DDS.  If form
factor is important then get DDS.  For further information try
comp.periphs or comp.periphs.scsi.

One last comment that I probably shouldn't make, but am going to
anyway.  If you want responses on notes, then buy DDS.  I have never
seen any response from Exabyte in notes.

Mark Simms

----------------------------------------------------------------------
Opinions expressed are my own and are not intended to be an official
statement by Hewlett-Packard Company
----------------------------------------------------------------------
Name:         Mark Simms
Profession:   Software Engineer
Occupation:   Research and Development
Organization: Hewlett-Packard Computer Peripherals Division
Unix-mail:    mark%hpcpbla@hplb.hpl.hp.com
----------------------------------------------------------------------