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Does hardware compression impact backward readability?

Andrea Wachter
Occasional Visitor

Does hardware compression impact backward readability?

If a DDS-x DAT tape is written with hardware compression enabled, can I be 100% sure that
the hardware compression will not prevent the tape being read by later models and versions of DDS drives, even if the time span between the two models is several years?

Phillip Williams_2
Respected Contributor

Re: Does hardware compression impact backward readability?


You are asking what the future looks like! Anyone who suggests you can be 100% certain of any prediction, certainly for several years out, should perhaps be treated cautiously...

However history shows that usually such features as hardware compression may/will be enhanced but almost always in a "backwards compatible" way - i.e.the new box can read/work with/handle the old stuff.

So you should be OK but, remember the 3 rules of computing:
a) Take a copy
b) Take another copy
c) take another copy in a different way & put it (physically) somewhere else..



The world is divided into 10 types of people: Those who understand binary and those who don't
Joshua Scott
Honored Contributor

Re: Does hardware compression impact backward readability?

The current generation of DDS, DDS-5, can read all the previous generations from DDS up to DDS-4. There doesn't appear to be any reason why this will not continue.

Given that I still see DDS-1 drives in use (14 year old technology), it is reasonable to assume that the current DDS-5(DAT72) drives will be around a while as well.
What are the chances...
Stuart Whitby
Trusted Contributor

Re: Does hardware compression impact backward readability?

You'll never guarantee this 100%. However, as long as people are supporting DDS, you should be able to guarantee that you can open a bug on it and get the backward compatability problem fixed at a firmware level.

If this is a big worry for your organisation, get an EMC Centera or similar. The whole point of it is that it will allow you to store every version of a file for years to come. Well, that's *one* point of it, anyway - I'm sure EMC Sales could come up with more :)
A sysadmin should never cross his fingers in the hope commands will work. Makes for a lot of mistakes while typing.
Andrea Wachter
Occasional Visitor

Re: Does hardware compression impact backward readability?

Well, the question behind my question is:
If someone's server + tape drive are stolen and they need to buy a new drive to restore their system from tape: could there be cases where having written the tapes using hardware compression prevents them from being readable on the new drive ?
Can we therefore safely advise people to use hardware compression ?

Thanks in advance,
David Ruska
Honored Contributor

Re: Does hardware compression impact backward readability?

If your replacement drive can backwards read the phsyical format, it's probably safe to assume it will also handle the compression within that format. I don't know of any cases where one was provided without the other.

Note: some new tape technologies limit how far back they read as far as physical formats (e.g. SDLT600 will only read back to SDLT320 and VS160).
The journey IS the reward.
Leif Halvarsson_2
Honored Contributor

Re: Does hardware compression impact backward readability?

There is always a limitation in backwards compatiblity with DDS drives, I don't belive hardware compression or not makes any difference.

Perhaps more important, DDS media in general is not very reliable. If you want to use medias for long time archiving you may look at DLT,SDLT or Ultrium technology.