On Wed, Sep 16, 2009 at 12:30 PM, Per Jessen <per@opensuse.org> wrote:
Brian K. White wrote:
How many write-read cycles does the best tape in the world accomplish before it fails? How many write-read cycles does even an ordinary hard drive accomplish before it fails?
That is what I mean. It is simply one metric among many.
Sure - we could also compare the physical size of the two, but it would be an equally inappropriate metric, IMHO.
The fact that a tape may be better by some other metric doesn't change this one.
True.
You are presenting an entirely different, also valid metric. A very good tape probably has a greater chance of reading without any errors after sitting around for 20 years than a hard drive. Greater but still nowhere near great. Even 99% chance is not great at all compared to what a hard drive does every second.
And really, who knows, maybe that tape and the hard drive have exactly the same chance after sitting around 20 years.
_I_ know. The tape wins hands down. There are many industries where documents and data must be kept for 10/20/25 years, sometimes even longer. The latter are usually microfilmed (or todays equivalent), the former are stored on tape.
Tape is far more reliable than disk if both are sitting on a shelf. As you say it was designed for it. Disk was not. Most larger corporations that are moving to disk based backup don't put disks on a shelf (like HOSO users often do). They maintain them with power on in a raid setup. Then they routinely scan them for failed drives and replace the drives as they fail. In my opinion, that drastically raises the cost of keeping backups on disk and I am still a big fan of tape based backups, but a well maintained raid array should be equally reliable IMO. fyi: at our office, we actually do keep a lot of data sitting on powered off disks, but we also make tape backups we send offsite of the same data. We've had about 10 hard drives fail in the last year. ie. when we pulled the drives off the shelf and tried to use them, they would not work reliably. None of the tapes we have retrieved from offsite have failed. Our offsite tapes are mostly a combination of LTO-1 and LTO-3. Greg -- Greg Freemyer Head of EDD Tape Extraction and Processing team Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer Preservation and Forensic processing of Exchange Repositories White Paper - <http://www.norcrossgroup.com/forms/whitepapers/tng_whitepaper_fpe.html> The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org