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Re: Backup (hardware) for Linux



On Tue, 14 Jul 1998 08:48:14 -0700 (PDT), Ira Abramov <ira@scso.com>
wrote:

>
>On Tue, 14 Jul 1998, Udi Finkelstein wrote:
>
>> >I never used DDS-3, but since I live in a very high-tech area and don't
>> >see DDS-3 in the stores, I'm guessing it is still very expensive and rare
>> >in Israel too. We're doing really fine here with a DDS2 tape changer
>> 
>> Nope. DDS3 cassettes are here and cost about 120 NIS + VAT. DDS2-120
>> cassettes which have 1/3 the capacity costs about 60 NIS + VAT, and
>> DDS2-90 (capacity is **half** of DDS2-120, NOT 3/4 of DDS2-120!) costs
>> about 30NIS + VAT, and DDS2-60 (2/3 of DDS2-90) costs a few shekels
>> less than DDS2-90 and are not cost effective.
>
>60 and 90 meter tapes are DDS1 tapes, that's why they are cheaper
>(different magnetic dust) and that's why the capacity differance.
>
>ok, getting off topic here, let's wrap it up.

Since we have started this, I'll finish it once and for all:

Tapes:
DDS1:
No hardware compression
Use 60m and 90m medias for 1.3GB/2.0GB respectively.
Can't read any other media, or DDS1-DC compressed data.
Speed is usually x1, i.e. 170KB/s

DDS1-DC:
Includes hardware compression
Use 60m and 90m medias for 1.3GB/2.0GB respectively, or 2.6GB/4GB if
compression is applied (the 1:2 ratios are the industry standard
numbers and may vary, typically for the worse...)
Can't read DDS2 or DDS3 media
Speed is usually x1, or slightly faster if compression is used.

DDS2
Includes hardware compression (I've never heard about a DDS2 drive
with no compression engine built in)
Use 60m,90m medias for 1.3GB/2.0GB respectively, or 2.6GB/4GB
compressed.
Use 120m media for 4GB native, 8GB compressed. Notice the 3:4 length
ratio and the 1:2 data ratio compared with 90m tapes. 120m tapes use a
different material/encoding/data rate.
Can't read DDS3 media.
Speed is x3 in HP1533/1599 drives, and x? on other drives (I think
Sony does x2). Again, Compression may make this faster.

DDS3
Includes hardware compression
Use 60m,90m medias for 1.3GB/2.0GB respectively, or 2.6GB/4GB
compressed.
Use 120m media for 4GB native, 8GB compressed.
Use 125m media for 12GB native, 24GB compressed. DDS3 tapes use even
higher density than DDS2.
Speed is x6 in HP1536 drives, and about the same on **most** other
drives. Again, Compression may make this faster.

Udi