Archive Status and Cache-A

[Tom Goldberg]

Hi Whitney,

I will defer any questions about how CatDV is tracking archiving tapes to those experts, but would like to provide answers about lost space.

Data tape can lose space for a wide variety of reasons:

Dirty heads or poorly performing tape decks as well as network connection issues can cause large amounts of lost space due to the need to re-write data that didn’t get written correctly (LTO does read-verified writes, checking every bit and rewriting it if it didn’t get onto tape perfectly).

Small amounts of lost space such as your 800MB out of hundreds of GB are usually due to less serious issues. Every time you write a single file, the deck must rewind, find the end of data and leave an empty block and markers for the start of new data. Each write session creates a tar package (what we call a tarball) and those tarballs have wrappers that use up a small amount of space as well. Thus the more sessions you have, the more these small losses add up and the more net loss you will see.

If you grab a whole stack of files and archive them together, the less space loss you are likely to see. You might even see a negative space loss (space gained through lossless compression in the deck).

You are welcome to contact our support group and have us evaluate the health of your tape drive if you have concerns about that (as long as you are under warranty).

Tom Goldberg
Cache-A Corporation
602 Park Point Drive
Golden, CO 80401
mailto:tom.goldberg@cache-a.com
https://cache-a.com

[Whitney Sickels]

Ah, that answers it then. I was archiving often, instead of all at once. Would it make sense to consider the vtape the backup until we reach almost 1.5 TB and then archive to tape all at once?

Regardless, I think we need support! I just checked the first LTO we put in (that I thought was full when it asked for another tape – as we were spanning), but there was only a very small amount of data on it!

Will you be at IBC in Amsterdam this year by any chance?

[Tom Goldberg]

We recommend a max target of 1425GB per LTO-5 tape to assure room for the TOC, and yes, doing it in fewer sessions is better, although you don’t have to do it all at once.

We are happy to look at your deck and any suspicious tape – please contact our support group as outline on our web site here

Yes, I will be at IBC in our new stand in hall 7 booth 7.E06!

Tom Goldberg
Cache-A Corporation
602 Park Point Drive
Golden, CO 80401
mailto:tom.goldberg@cache-a.com
https://cache-a.com

[Aat Aar]

I am facing a problem of 300Gbs to 400Gbs of Space lost in LTO 5.

[Tom Goldberg]

Large amounts of space lost are typically due to a tape drive that needs to have a cleaning tape run on it. Give that a try and see if your next archives aren’t better… if not, you have have a hardware issue and will need a support connect session so we can evaluate the health of your drive.

Note that if you are seeing a negative space lost, it simply means that you have compressible material and the tape drive’s internal lossless hardware compression engine is saving you room on the tape.

Tom Goldberg
Cache-A Corporation
433 Park Point Drive #285
Golden, CO 80401
mailto:tom.goldberg@cache-a.com
https://cache-a.com

(FYI – this really should be posted as a new topic and in the “Archiving and Backup” Forum)

[Aat Aar]

Thanks for the reply

I connected the machine with cache-a support they tested all the hardware, and found that the 1st drive is failing,
But is that why i am facing Large amount of Space Lost ?

[Tom Goldberg]

I’m sorry but there is no way to tell from this amount of information – please email me your case number and I’ll look into it.

Tom Goldberg
Cache-A Corporation
433 Park Point Drive #285
Golden, CO 80401
mailto:tom.goldberg@cache-a.com
https://cache-a.com