Tape backup: why the end of tape is reached

User Help, discussion of features, issues, and general topics about Uranium Backup.

Moderators: Davide Costantini, Romana Romandini, Andrea Ciotti, Administrator

Uranium Backup Team
User avatar
Posts: 1401
Joined: Mon Oct 03, 2005 4:33 pm

Tape backup: why the end of tape is reached

Postby Administrator » Mon Feb 18, 2013 12:50 pm

As a software company that provides backup solutions, we find ourselves handling the problems of our customers. With tape backups it happens often that the end of tape is reached apparently too soon or that too many bytes of the cartridges are written compared to the data backed up.

Tapes are cheap and reliable storage devices but their maximum capacity is affected by several variables. This article has been written to help your troubleshooting.

Tape capacity and data compression

There’s a lot of confusion regarding the advertised and effective capacities of the tapes. Usually the cartridge box shows the maximum capacity achievable through a compression ratio of 2:1. In a nutshell, it means manufacturers assume that 800GB of data can fit into a 400GB – real capacity – tape.

This scenario is more than optimistic and we have to consider that most of today’s data formats – like .docx, .png or .jpeg – are already compressed: with these files there would be no gain and sometimes the compression will waste space instead of saving it. Furthermore different compression algoritms produce different results depending on the data copied.

A far more reasonable “optimal tape capacity” stays in a range between the physical one, 400GB for a standard LTO3 tape for instance, and a low compression ratio like 1.2:1 or 1.3:1 (if compression is enabled).

Data flow from the SCSI host to the tape drive

In order to efficiently write on the cartridges, tape units need to receive a consistent and fast-enough data flow. The drives write data in big chunks called frames and when the flow is interrupted they fill them with zeroes, wasting the tapes capacity.

Bottlenecks and/or misconfigurations of your hardware and network can amplificate the wasted space on your tape.

Write errors

When the tape drive detects write errors it has to re-write the data. Old tapes, dirty read-write heads or a faulty drive can waste most of the available capacity. It’s important to regularly clean the drive heads in order to maintain the optimal capacity.

How to fix “capacity issues”

First of all check the tape effective capacity. If you can’t push 580GB of data into a 400/800GB (real/compressed) LTO3 tape there’s no real problem here. You have to split the backup into multiple tapes.

Check the health of your drive and tape with a maintenance software like HP Library and Tape Tools. Then clean the read-write heads with the cleaning tape cartridge.

If the problem persists investigate the consistency of the data flow between the storage disks and the tape drive. Reducing the loads of the storage and network hardware can help containing the amount of data written.
Uranium Backup Support

Posts: 3
Joined: Mon Jan 13, 2014 8:46 pm

Re: Tape backup: why the end of tape is reached

Postby swd » Mon Jan 13, 2014 8:49 pm

But how can I split the backup into multiple tapes?
Tried to backup more data to a tape than possible, and just ended the backup with an error.
So I would like to know how exactly I will be able to split the backup over multiple tapes.

User avatar
Posts: 490
Joined: Fri Dec 21, 2012 12:17 pm

Re: Tape backup: why the end of tape is reached

Postby Christian Del Moro » Tue Jan 14, 2014 10:48 am

Hi,

Uranium Backup doesn't support append and multi-session backup on the Tape.

Posts: 3
Joined: Mon Jan 13, 2014 8:46 pm

Re: Tape backup: why the end of tape is reached

Postby swd » Tue Jan 14, 2014 12:06 pm

Why? It's a simple option which even the old NTBackup has, and should make a lot of people happy.
These days files to backup are sometimes big and without tape-spanning it's impossible to store them on tape.
We have single files of over 2TB that we want to archive on tape, and that is not possible without this option.
It is kind of strange to store them for example in RAR files of 800GB to be able to arhive them into LTO4 again,
while this option should be available in the backup software.
It is maybe a little bit more risky than without spanning, but that is a choice people should make for their own, sin;t it?

User avatar
Posts: 490
Joined: Fri Dec 21, 2012 12:17 pm

Re: Tape backup: why the end of tape is reached

Postby Christian Del Moro » Mon Feb 10, 2014 5:26 pm

I know but at the moment this feature isn't available however is present in our roadmap but I can't say a date

Posts: 3
Joined: Mon Jan 13, 2014 8:46 pm

Re: Tape backup: why the end of tape is reached

Postby swd » Fri Aug 15, 2014 8:55 am

Is there a planning when to add this spanning feature, by now?

User avatar
Posts: 490
Joined: Fri Dec 21, 2012 12:17 pm

Re: Tape backup: why the end of tape is reached

Postby Christian Del Moro » Wed Aug 20, 2014 8:45 am

Hi,

at the moment there isn't news about the development of this features. Our development team is working about other peculiarity such as Hyper-v virtual machines backup and cloud backup.

Regards

Posts: 1
Joined: Wed Feb 10, 2016 6:55 am

Re: Tape backup: why the end of tape is reached

Postby Alexander812 » Wed Feb 10, 2016 7:01 am

This feature is very, very necessary.

Return to Technical Support ENG

Who is online

Users browsing this forum: Bing [Bot] and 1 guest