Tape 'size of stored data' metric - what does it really mean?

Last post 09-29-2020, 9:03 AM by Dataprotectionshow. 1 replies.
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  • Tape 'size of stored data' metric - what does it really mean?
    Posted: 09-25-2020, 10:29 AM

    Hello experts,

    I have a question on the 'size of stored data' statistic one sees when viewing tape library media, and what it actually means.

    Scenario 1:

    I have a backup subclient that I setup to write directly to tape .. a storage policy where the primary copy is on tape, no disk-library involved.  The SC has 1.7TB of content, and after the backup completes and I look at the tape cartridge (assuming it used a new/empty cartridge), it shows the 'size of stored data' as 1.7TB. It all makes sense.

    Scenario #2:

    I run the exact same backup subclient to a different storage policy which has a disk library (in our case, on a hyperscale) as the primary copy, then is setup with a secondary copy for tape.  The SC backup to the disk lib shows it backed up 1.7TB of application data (though only a comparatively small amount was actually 'written' due to dedupe).  Next I manually run an auxcopy to make the tape copy.  Afterthe auxcopy completes (again, assuming it selected a new/empty tape cartridge), the 'size of stored content' for the aux tape media shows ~470GB of data.  How can that be?  I would think that for aux-to-tape that the source data would have to be completely re-constituted/re-hydrated.  In other words, the aux job should have sent 1.7TB of non-deduped, non-compressed to be written to the tape drive.  Am I wrong here??  What am I not understanding in this, or is the 'size of stored content' metric not what I think it should be?

    One reason I'm asking this is that in scenario #1, the backup-to-tape takes ~2hrs to complete, whereas in scenario #2 the aux-2-tape was taking about half that time.  Something seems odd here, and it's probably just something I don't fully understand.  I do know the tape data is indeed recoverable as I've done that before in testing.

    Thx in advance for any replies

  • Re: Tape 'size of stored data' metric - what does it really mean?
    Posted: 09-29-2020, 9:03 AM

    Is Hardware compression turned on on all Data Paths involved in each copy?

    Right Klick Primary Copy -> Properties -> Data Paths -> Property -> Hardware Compression,

    do that for all Copies.


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