Thursday, 28 September 2006

To Copy or not to Copy?

Sony have just announced the availability of their next generation of AIT; version 5. More on AIT here Speeds and feeds; 400GB native capacity, 1TB compressed and 24MB/s write speed. The write speed seems a little slow for me but the thing that scares me more are the capacity figures. 1TB - think about it 1TB! That's a shedload of data. Whilst that's great for density in the datacentre, it isn't good if you have a tape error. Imagine a backup failing after writing 95% of the data of a 700GB backup - or more of an issue, finding multiple read errors on a TB of data on a single cartridge.

No-one in their right mind would put 1TB of data onto a disk and hope the disk would never fail. So why do we do it with tape? Well probably because tape was traditionally used as a method of simply recovering data to a point in time. If one backup wasn't usable, you went back to the previous one. However, the world is a different place today. Increased regulation means backups are being used to provide data archiving facilities in the absence of proper application based archival. This means that every backup is essential as it indicates the state of data at a point in time. Data on tape is therefore so much more valuable than it used to be.

So, I would always create duplicate backups of those (probably production) applications which are most valuable and can justify the additional expense. That means talking to your customers and establishing the value of backup data.

Incidentally, you should be looking at your backup software. It should allow restarting backups after hardware failure. It should also allow you to easily recover the data in a backup from a partially readable tape. I mean *easily*, not oh, it can be done, but its hassle and you have to do a lot of work. Alternatively, look at D2D2T (

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