On Feb 6, 2008 12:07 AM, Bill McGonigle <[EMAIL PROTECTED]> wrote: > I often ask, "if your building has burned down, can you afford to > lose a week's worth of data?".
Yah, the only sane way to determine one's desired backup interval is by comparing cost of implementing a given interval with the cost of loosing the data over that interval. How much does loosing a day's worth of data cost? A week? An hour? How much more hardware will you have to buy to support hourly vs daily snapshots? And so on. > In my experience I've had to deal with more bad backup tapes than > backup drives. I find quality tape drives to be quite reliable within their rated specs. I suspect one problem is people aren't really conscious of those specs. For example, IIRC, DDS4 tapes are rated at 2000 pases. If any given spot on the tape has passed over the read/write head more than 2000 times, it is time to retire the tape. Since the tape is divided into tracks, and smart people do a full read-back-compare to verify after writing, a single backup run might mean 10 or 20 passes, and maybe even more on a "hot spot" like a logical tape label. I suspect Travan is rated at one pass. ;-) I don't know that there's much in the way of an established body of evidence for the reliability of removable HDDs which are frequently transported. It's still a relatively young idea. It will be interesting to see how that develops. I know I see more HDD failures in laptops than desktops, but they're more often spinning when moved, so that's not apples-to-apples. > And very few folks write FEC data to the tapes ... The better drive technologies include FEC/ECC. I believe both LTO and SDLT do. They also include "read while writing", where the drive reads the data back in immediately after it writes it, to make sure it got written properly. -- Ben _______________________________________________ gnhlug-discuss mailing list gnhlug-discuss@mail.gnhlug.org http://mail.gnhlug.org/mailman/listinfo/gnhlug-discuss/
