8mm vs. 4mm
>braida@cmc.ca (Gary Braida) writes:
>
>>Media Costs
>> 8mm $16 (112m data grade)
>> 4mm $27 (120m data grade)
>
One thing here too is, that the 120M tape for 4mm is the longest
you can buy. The tape drives should accept 60M and 90M tapes too which are
cheaper. 90M tape stores 2 gig, 60M stores 1.3 gig, 120M I think is 2.7
gig, right? This is all without compression.
>
>>Which one is faster
>> The only real concensus on this one is that 4mm drives seek much
>> faster than 8mm drives.
>That's true, but 8mm have about twice the transmission rate of 4mm at
>the same level of technology, which is not surprising given that
>they're twice as wide. For dumps, transmission rate is more important
>than seek time.
>
This is interesting, because my dumps to my 4mm tape drive have
always "felt" faster. But I have never really tested it (of course my 8mm
and 4mm are on different machines...).
>
>> If we crunch the drive and media costs to find where the breakover point
>> is we'll find that if you plan to use a large number of tapes, more than
>> 180, then its more cost effective to use 8mm.
>
>The exact number of course depends on the costs. But I noticed that
>your analysis neglected the fact that (again, at the same level of
>technology) 8mm tapes hold twice what 4mm tapes hold, so you overstated
>your 8mm cost per megabyte by a factor of 2. If you're a heavy user
>(as opposed to someone who usually doesn't fill up the tape), this is
>another advantage for 8mm.
I don't find this to be true. 4mm tapes can hold less, but they can
also hold just as much. (See the first paragraph on tape lengths and
storage capacity.)
I am not up on the compression 4mm tape drives, but I know there is
an HP tape drive that can store up to 8gig, not sure on what tape. I assume
120M tapes.
Later,
Mike mikeg@asylum.gsfc.nasa.gov
