SUMMARY: Exabyte 8500XL 8mm Tape

From: Mark Sturtevant (
Date: Tue Mar 12 1996 - 13:36:13 CST

Thanks to all who responded:
 Casper Dik <casper@holland.Sun.COM> (Brett Lymn) (Rob Allan) (Timothy Henrion) (Richard J. Niziak)
 David G Wiseman <>
 Jens Fischer <> (Mark S. Anderson)
 Cola Allen <>
 Tom Schmidt <>

Here is my original message:

>Hey Everyone,
>I am having some trouble getting 14GB out of a tape using ufsdump with
>Exabyte's 8500XL 8mm tape drive, the 8500XL is supposed to be able to get
>14GB on a 160m tape but it stops at around 10GB. Here is the command I am
> ufsdump 0ubf 126 /dev/rmt/0c {partition}
>The system is a Sparc 20 running Solaris 2.4 with kernel patch 101945-34.
>Is there another device I should be using for more compression? I see
>in the Solaris 2.5 "st" man page is has a "u" device that is says is
>"ultra/compressed" but it doesn't say if it is compatible with the
>8500's. Is this also the case for Solaris 2.4?
>All/Any input would be greatly appreciated.
>Thanks in advance for all your responses.
>Mark Sturtevant <> <>
>Unix Systems Administrator
>P A R A N E T

The General concensious is that 10-11GB on a 160M tape using the 8500XL is
normal, the 14GB is a virtual number that the company came up with using
data that probably wasn't compressed and is based on a 2 time compression ratio,
the real world ratio (with a mixture of data types) that most of the people
wrote me back with is 1.6, which gives you around 10GB.

The following are the responceses I received:

From: Casper Dik <casper@holland.Sun.COM>

On my systenm, the u devices are the same devices as the c devices.

From: (Brett Lymn)

It really depends on the data you are backing up. The native
(i.e. uncompressed) capacity of your tape drive with 160M tapes is
7Gig. The 14Gig comes from exabyte (and others) assuming a 2:1
compression ratio. In my experience, with a normal mix of text and
binary files, you should expect about 1.5:1 for a compression ration
which is about what you are getting on your tapes.

Brett Lymn, Computer Systems Administrator, AWA Defence Industries
  "Upgrading your memory gives you MORE RAM!" - ad in MacWAREHOUSE catalogue.

----------------------------------------------------------------------------- From: (Rob Allan) X-Status:

The actual capacity of this type of tape is 7Gb, with 2X compression, you'll get 14 Gb. It is very rare to get this level of compression if you are backing up a file system which contains binaries, already compressed files, etc.

---------- Rob Allan | Ontario Hydro | Tel. (416) 592 4195 Toronto, Ontario, Canada | Fax (416) 592 4966 ----------------------------------------------------------------------------- From: (Timothy Henrion)


I've found Exabyte's compression claims to be a little exaggerated. My guess is that you won't get more on a tape than you are already getting.


-- Tim Henrion Computer Sciences Corporation ----------------------------------------------------------------------------- From: (Richard J. Niziak)

The 14 Gb capacity is their best case scenario, unless you are backing up raw databases or just text files, I doubt that the compression algorithm that they use will get you more than 10-11Gb on the tape..

BTW the "u" or "ultra" device is only for the 4mm dat drives...

-Rick Niziak Systems Consultant Hammerhead Consulting ----------------------------------------------------------------------------- From: David G Wiseman <>

Five'll get you ten that the data you were trying to back up was already compressed somewhat... I've already encountered this on all of my compressed backup drives: we do a lot of image/vision work and those files are already so compressed that the drive s/w cannot compress them further. It got so bad here that I don't even try to compress any more.

-- magi David Wiseman, Network Manager e-mail: Department of Computer Science The University of Western Ontario fax: +1 519 661 3515 London Ontario Canada N6A 5B7 voice: +1 519 679 2111 x6879 ------------------------------------------------------------------------------- Supporting Windows is like buying a puppy. The dog only cost $100, but we spent another $500 cleaning the carpet. -- Marc Dodge ----------------------------------------------------------------------------- From: Jens Fischer <>

14 GB is an estimated value which relies on a compressin factor of 2. As compression factors are varying depending on the data which is compressed the 14 GB capacity is not always true. You may reach this capacity when you are storing large ascii files. In our site we are experiencing a compression factor of about 1.5, which leads to an amount of 10.5 GB per tape. You should also be aware of the space which is produced between two logical volumes on one physical tape, which needs an additional amount of some MB each.

Hope that helps

Regards - Jens Fischer

I User : Jens Fischer Department : DV-Anwendungsentwicklung Technik I N A Company : INA Werk Schaeffler KG Address Industriestrasse 1-3 A D 91074 - Herzogenaurach Phone : (+49)9132-823262 FAX : (+49)9132-824953 e-mail :

----------------------------------------------------------------------------- From: (Mark S. Anderson)

First of all, you will not get 14GB. Due to overhead, you will only be able to use approximately 90% of the tape for data. So, you're down to 12.6GB max. Then, as you probably know, the 14GB figure ASSUMES a 2:1 compression ratio. You may or may not achieve this. If you are getting 10MB on the tape, and assuming a 10% loss as mentioned above, then the compression ratio is about 1.6. This is not unreasonable.

How I estimated the compression ratio: You have a tape that will hold 7GB without compression. If 10GB is 90% of the tape, then the tape is holding 11.11GB. The compression ratio is 11.11/7 ~= 1.6

Mark Anderson ---------------------------------------------------------- Mitretek Systems, Inc. 7525 Colshire Drive, MS Z420 voice: (703) 610-1762 McLean, VA 22102 FAX: (703) 610-1561 ----------------------------------------------------------------------------- From: <>

Don't ever believe any supplier's claims about how much data fits on a tape using compression. When you go back to them they'll simply say "well, it depends on your data". Some data is more compressible than other data. We have a large hetrogenius network with what I consider to be fairly 'normal' data, and we have never ever managed to get the advertised capacity onto any compressed tape device from any supplier. It makes me wonder what kind of data they use in their tests to make these claims. ----------------------------------------------------------------------------- From: Cola Allen <>


The type of data you are writing to tape determines the amount of data that can be stored. ASCII data will compress significantly whereas graphic files like GIF and binary files and obviously compressed files will not compress much whether compressed by h ardware or software. I believe the 14GB figure is an estimate based on some reasonable mix of data. 10GB doesn't sound to far out depending on your data.

Hope this helps.

Best regards, ^ ^^ ^ ^^ ^^ ^ ^ +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ | ||^ | || ||^| | |e-mail| |^||| | | ||||^| |phone (714)961-6553 | ||||| __o |||||| +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+ . .~_( <, .~. .~. . _ (*)>(*) _ _ _ _ Cola Allen . . . . . . . . .

----------------------------------------------------------------------------- From: Tom Schmidt <>


The 14GB capacity is assuming a 2:1 compression ratio. If your filesystem contains a lot of files that are not highly compressable (.zip, .gz, .Z, .gif, .jpg, etc.) then you may not achieve this ratio of 2:1. 7GB is the uncompressed capacity. On my 8500XL, I typically get about 11GB on a 160m tape. Your mileage may vary. :)

I have not tried the "u" option on the tape drive with my 8500XL. I just use the "c" option.


-- _____ ___ Tom L. Schmidt, Manager, Component Characterization | | / \ Micron Technology, Inc. | | \___ 8000 S. Federal Way P.O. Box 6 Mail Stop 376 | | \ Boise, Idaho USA 83707-0006 | |____\___/

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