Date: Fri, 05 Apr 2002 11:15:40 -0700 From: Brett Glass <brett@lariat.org> To: "f.johan.beisser" <jan@caustic.org> Cc: freebsd-chat@FreeBSD.ORG Subject: Re: backup solutions Message-ID: <4.3.2.7.2.20020405110535.0308a630@nospam.lariat.org> In-Reply-To: <20020405092135.A96787-100000@pogo.caustic.org> References: <4.3.2.7.2.20020405084626.00b8e360@nospam.lariat.org>
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At 10:53 AM 4/5/2002, f.johan.beisser wrote: >as far as the electrical/mechanical interface goes, a harddrive still has >head crashes, Very rarely. And it's not as if you're taking the media out, as you do with tape. >ok, this true, we live in a giant magnetic cage. > >this is also true: i've taken audio tapes that have sat in my garage for >10 years, popped them in to a tape deck, and listened to them. with no >significant loss of quality. The tolerances on these are, of course, much looser. Tape drive vendors, who are locked in fierce competition and must keep up with increases in hard disk sizes, almost always skate close to the edge of what the current technology can handle. And because restores from backup tapes are relatively rare and the tapes are overwritten regularly, they don't need to maintain the reliability levels and long-lasting data retention that hard drive manufacturers must. >i've had a 10 year old hard drive that i can't recover anything from, due >to the lack of an interface for it. I have WD1003 cards in my lab to this day. But if you're doing archival backup, you'll have bigger problems with tapes than with disks, as tapes MUST be refreshed regularly. >media aging is an issue aswell >(remember a couple months ago, about that laserdisk in england?), how can >you gurantee that in 10 years, you'll be able to recover your data from >that media? Tape ages more quickly than hard disk platters (which have a hard surface that's usually deposited or grown on). >> Hard drives have the same property. And damage is less likely because >> they're fully enclosed. > >what about the electronics on the "underside", where the controller is? I have 20-year-old PC boards that still run fine. >> If you're worried about this, use the Microsoft FAT format, which >> virtually everything can read. > >i think just about anything i'm likely to use can read that format. i >still wouldn't trust it for backups. We use PKZIP on MS-DOS FAT for archival backups. It'll be readable many decades from now. >> Tapes do not last as long. And tape cartdridges are often as expensive >> as entire hard drives! > >they don't? in my experience, they last MUCH longer than hard drives. >years longer. If you use tapes for daily backups, they wear out much faster. If you use them for archival backups, they are subject to flaking, swelling, and other nasty problems. >As far as cost goes, yes, usually the cost of equivelent tape storage >(let's say 50gb, uncompressed) will be more than the hard drive. is this >the fault of tape manufacturers? Yep. They give away the drive and make money on the media. Just like printer vendors. >no, i think higher than tape. for example: in a one month period, i'd had >3 drives in a RAID array go bad. that is drive 1 in the RAID5, and both >the replacement drives. Anecdotal. The MTBF of disks is much longer. >> The MTBF of hard drives is so much longer that they're a net win. > >my experience, with large systems and small, is that the Mean Time Between >Failures is much lower on older tapes, than older drives. on newer drives, >i've had quite a few fail right out of the box, and have yet to see a >failure of any tape "just out of the box" (in the last year). I've gotten many tapes with lots of defects -- some which are unwritable. Disk drives, especially after a surface analysis and initial burn-in, are much more reliable. --Brett Glass To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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