Asset ID:	1-72-1013590.1
Update Date:	2011-07-28
Keywords:

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Solution Type  Problem Resolution Sure

Solution  1013590.1 :   VTL - Virtual tapes do not fit on physical tapes using VTL defaults sizes  


PreviouslyPublishedAs
219139

Applies to:

Sun StorageTek VTL Storage Appliance - Version: 4.0 - Build 1221 to 4.0 - Build 1221 - Release: 4.0 to 4.0
Sun StorageTek VTL Plus Storage Appliance - Version: 1.0 - Build 1323 to 2.0 - Build 1656   [Release: 1.0 to 2.0]
Sun 386i Sun/OS
.
***Checked for relevance on 27-07-2011*** (dd-mm-yyyy)

Symptoms

• Virtual tapes do not fit on physical tapes.
• VTL default virtual tape sizes do not fit on physical tape.

Changes

Problem may occur when VTL administrator  increases max size of virtual tape, making it too big to fix on real tape. 

Cause

Virtual tape is too big to fit on real tape.  Compression may be a factor.

Solution

  There are many customer issues reported of not being able to copy/move all the data from virtual tape to the physical tape even though the both tape sizes are same. There are some guide lines to set the capacity of the tapes which addresses this issue and how to take care of it.

In the configuration wizard, in creating virtual library step, while specifying the tape properties, make sure to follow the guidelines below for the Maximum Capacity parameter of the tape:

1. You can set any Maximum Capacity if you are not planning to export data from Virtual to physical tape.

2. If you are going to export data to physical tape you can use any Maximum Capacity if you are not using VTL's hardware or software compression. But if you enter a capacity that exceeds the native uncompressed capacity for the media, you will not be able to export to physical tape.

3. If you are going to export data to physical tape and are using VTL's hardware of software compression, the Maximum Capacity should be set to 10-15% less than the uncompressed capacity of the selected media, since VTL's compression algorithm can vary depending upon the dataset. Certain file types (ZIP, PDF, GIF, RAR, wtc.) are already compressed and connot be compressed further.

For more information on the compression ratio, please see 1132963.1.

VTL tape size is calculated with base2 rather than the base10 that physical tapes are calculated by.  
For example, a 500GB tape in VTL is larger than 500,000MB - it's about 512,000MB.  The actual physical
tape size is going to be 500,000MB.
This calculation was changed to base10 in VTL Plus Build 1323 - no fix for VTL2 systems with  
Automated Tape Caching.

References

<NOTE:1132963.1> - VTL - Is compression on disk and virtual tape the same?

Attachments

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