Date: Fri, 5 Apr 2002 09:53:25 -0800 (PST) From: "f.johan.beisser" <jan@caustic.org> To: Brett Glass <brett@lariat.org> Cc: freebsd-chat@FreeBSD.ORG Subject: Re: backup solutions Message-ID: <20020405092135.A96787-100000@pogo.caustic.org> In-Reply-To: <4.3.2.7.2.20020405084626.00b8e360@nospam.lariat.org>
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On Fri, 5 Apr 2002, Brett Glass wrote: > At 10:08 PM 4/4/2002, f.johan.beisser wrote: > > >my own preference is tape. > > > >tape.. > > > > 1. tape transfers between machines, and usually OSs fairly well. > > I've found that tape drives often do not read tapes written on other > drives reliably. The electrical, rather than mechanical, interface of > a hard drive eliminates that problem. this is a matter of having good hardware, i believe. i've had very few problems with Sony AIT and AIT2 tapes. older DLT-IV tapes seem to be somewhat inconsistent in quality. Newer Fujifilm DLTs have been very good to me. as far as the electrical/mechanical interface goes, a harddrive still has head crashes, and as with anything that's getting cheaper (IDE, for example) the overall reliablity is going down. > > 2. tar(1) is usually very transferable between various flavours > > of UNIX. > > tar(1) can be used on disks as well as tapes. true, it can even be piped through ssh, if one wants. > > 3. tape, and tape drives, tend to be more reliable, > > I don't find this to be so. Tapes seem to become unreadable in less time, > in part due to "print-through" and in part due to the fact that we're all > living on a magnet (the Earth) and tape is not shielded from this and > other magnetic fields. (Disk drives have a protective metal case.) 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. i've also taken 15 year old DLT tapes, that've been stored inside of a datacenter, and had no problems getting the data off of them. 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. 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? > >and even if > > one part of them is damaged, you can usually recover data > > with little effort. > > 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? > >hard disks.. > > > > 1. difficult to transfer between OSs. > > 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. > > 2. difficult to transfer between machines > > If removing the cover and inserting two cables is an issue, try > the many readily available "quick swap" mounts used in RAID > systms. this is still more effort than taking a tape to a drive, and slotting it. > > 3. damage prone (head crashes, bad sectors as they get older > > etc). > > 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. 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? and yes, tape storage media has not kept up with hard disks in capacity and cost, and the "average" computer sold these days has a 20gb hard drive. more than most tape. > > 4. even in redundant environments, the potential for dataloss > > is very high. > > No higher than for tape! 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. in comparison: i've had 3 tapes go bad due to age and harsh environments in the last 6 years. those tapes were already marked as being "funky", so it wasn't a nasty suprise. > > 5. it's *very difficult* and *very expensive* to recover data > > from a damaged hard drive. > > 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). of course, the usage of a tape vs an HD is also an issue here. while a drive may be designed for 300,000 hours, it's far more likely to be used for all that time, and under constant use. my average tape has a lifecycle of 60 read/writes, well below the MTBF for just the tape (not the drive). most tape drives are designed with 200,000 to 400,000 hours, and don't expect to be put under 100% usage. > Just IMHO, of course. we'll agree to disagree ;) -------/ f. johan beisser /--------------------------------------+ http://caustic.org/~jan jan@caustic.org "John Ashcroft is really just the reanimated corpse of J. Edgar Hoover." -- Tim Triche To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-chat" in the body of the message
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