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Used Capacity versus Data

We use LTO 800gb/1.6tb tapes but have noticed out used capacity versus data is significantly different. Most of the tapes are reporting used as 779.9gb of 781.5, but the data fluctuates between 490gb upto 548gb.

The job in question is set to hardware compression but why is the data so low?

1 Solution

Accepted Solutions
Accepted Solution!

...your best bet is to read

...your best bet is to read the TN below as this explains your options when labelling tapes...and the data is actually destroyed. Don't ask me why!

https://support.symantec.com/en_US/article.HOWTO22308.html

Thanks!

View solution in original post

9 Replies

Possibly because the

Possibly because the compression ratio is different for different jobs / tapes.

Also, was the tape drive cleaned recently (as a clean tape drive usually helps a bit with slightly improved compression ratios) ?
 

...the amount of data on disk

...the amount of data on disk is 490-548GB? Have you checked the compressions stats on the tapes in question? Anything showing .x:1 could mean that data is compressed already, and might be decompressing when being backed up to tape. Deduped data will always rehydrate, but compressed data in that store might be inflating in size.

Thanks!

This is one job and the

This is one job and the compression is the same for each tape from what I can see.

Drive is cleaned regularly, that was the first thing I did after reading around. I've read an artlicle that pkh wrote but I'm trying to get clarity to understand why the data written is so low compared to the native capacity.

Nine tapes in the job, the

Nine tapes in the job, the 'Data' column is reporting different for each, which ranges from 492.3gb to 546.3gb. Compression ratio field is 1:1

Or is the Data field just reporting how much data was written in the last job because if you media label a tape after the job the Data field reduces to 64k

 

Have a look @ this

Have a look @ this explanation - https://www-secure.symantec.com/connect/articles/tape-statistics-explained

And 1:1 ratio indicates no compression is being achieved.

Thanks but that's still not

Thanks but that's still not very clear. All it reports is how much data was sent to the tape, when exactly? (during the last job that used these tapes)

Also, if you media label a tape, it reports this tape 'Data' now as 64k, places it in scratch and you can no longer restore untill you Catalog. If you then Catalog it reports no backup sets were found on this media!

So now, are tapes that I've labelled after a backup has completed no longer part of the backup set or restorable as part of that set?

 

I suspec that labelling a

I suspec that labelling a tape actually erases it completely. Just check that out, and make sure the tape has a label BEFORE running a backup.

Or use barcodes instead.

Post a screenshot of your issue...

Thanks!

Well that's just great, when

Well that's just great, when you select 'label media', none of the prompts suggest that it will erase the tape!

If the tape has been erased, why does the 'Used Capacity' stay at 779.9GB of 781.5GB.

All I'm trying to do is understand what the various information fields means, as yet this seems very difficult for people to explain in simple terms, even the referrals aren't clear!

I think from now on I'll just leave the labelling because this software isn't capable of informing me what is going on!

 

 

Accepted Solution!

...your best bet is to read

...your best bet is to read the TN below as this explains your options when labelling tapes...and the data is actually destroyed. Don't ask me why!

https://support.symantec.com/en_US/article.HOWTO22308.html

Thanks!

View solution in original post