Doug Hughes <[email protected]> writes: > > Are there any tape systems that have a lower cost per gigabyte than > > 1TB or 1.5TB sata disks? > You don't offer much context to your question, but the answer is most > assuredly yes. It depends how you want to use your tapes. > > 1 1TB enterprise seagate SATA disk is $200-$245 online (actually about > 900GiB because they use power10 TB instead of power2) > 1 LTO4 (800GiB) tape is about $48 in quantity one (significantly less > in bulk)
Interesting. hm. and the drives look to be around $3000 before the robot. I do have a metric ton of 1gb fibre channel stuff laying about. But my experience with tape has been that it is way less reliable than even the crappiest consumer-grade drives you can find. This may be ignorance or incompetence on my part (I don't think I've touched a tape since I reached the age of majority) - but either way, for me, tape has been unreliable, and disk, while not completely reliable, fails in ways I've seen thousands of times before, ways that I can deal with. (more importantly, when data is corrupted on my spinning disk, my pager goes off. With tape, you don't know until bob in accounting wants that really important file, or the new guy wipes out the billing server.) See, the biggest reason why I don't use tape is that my experience has been that tape backups seem to fail at least one out of five tapes. (of course, this mostly comes from my experience as a tape monkey in highschool. Maybe it was just that the companies I worked for didn't have anyone that knew anything about tape. This was largely before I knew anything about anything. My job was usually to take the tape out of the server, put it on the bottom of the tape stack (usually in a filing cabinet) and put the top tape in the server, but of the 5 tape restores I saw during that period, 2 of them went off without a hitch, 1 of them required going back a month because of a corrupted 'level 0', and two of them were total losses.) Because I've never seen tape work reliably, when I am in control, I always provision spinning disk, as I know how to deal with failures in that arena. (and yes, you do need to checksum your disk data, and monitor your logs closely to deal with I/O errors. silent errors do happen... but they happen everywhere. You wouldn't run without ecc ram, would you? checksum your backups, and preferably your running disk.) It's possible that tape is just really sensitive to humidity (I've read that in dry areas ESD is a leading cause of tape failure. The Sacramento valley, where I spent my childhood and most of the parts of my career that dealt with tapes, can get pretty dry at times. All of the places I worked, at best, kept the tape in a locked filing cabinet. So it could just be ignorance.) if you are using raid (especially something like zfs that does checksuming on the block level, but even if you just do a md5sum that verifies periodically) and you monitor the damn things, (this means replacing the drive when you see I/O errors, Not just rebooting the box and saying you cleared the errors. Silent errors do happen, but the vast majority of disk errors on systems with ECC ram do leave spoor in the logs, it's just that most people ignore those errors that can be 'cleared' by a reboot.) consumer grade is probably 'good enough.' it's certainly much, much better than my experience with tape has been, and it gets your cost per gig almost down to the cost of tape. (I've worked with terrifyingly massive installations that used consumer-grade disk. The key is the ability to notice when you have disk errors and the ability to take any server out of production at any time without breaking anything, and then a few guys with shopping carts full of hard drives wandering the aisles of your data center. but for small shops, It's cheap to put a 16 bay supermicro in some far-off co-lo (or under the bed). just leave the disks in, and your total cost is usually less than the drive and tapes for equivalent capacity. > depending upon how many you buy and what your requirements are, tape > is still significantly cheaper than disk, especially once you add in > power for <x> TB of running disk. Tape wins in offsite archival as > well. yes, power is a big deal. you have a good point there. I would argue that spinning disk is also pretty convenient for off-site, though. spinning up a 16-bay supermicro under my bed (or in a co-lo on the other side of the globe) is pretty cheap, and I can automate the 'tape change' process as well as the 'restore file x from last week 'cause joe in accounting screwed it up' process, and I can easily have multiple levels of isolation. I guess you can probably do all the same things with a tape robot of sufficient capacity/scriptability, but writing a interface to the spinning disk system is trivial. Another advantage of disk is that I already know about disk (and if the new guy doesn't, she is going to learn fast or she won't be the new guy for very long.) so usually, a relatively inexperienced SysAdmin can come up with a reasonable backup solution using spinning disk. Something that lets joe in accounting retrieve the really important file he screwed up yesterday. Using tape, well, doing anything besides a full restore requires some specialized software, and at nearly all of the places I've worked, is simply not done. _______________________________________________ Tech mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
