>>>>> "Mark" == Mark Hahn <hahn@xxxxxxxxxxxxxxxxxxx> writes: >> RAID is no excuse for backups. Mark> I wish people would quit saying this: not only is it not helpful, Mark> but it's also wrong. You've got to be kidding, right? A backup is another aspect of data protection. RAID is another form. Both have their uses, and both should be used on any system with important data. You're just spouting the wrong thing here and I really dislike seeing it, which has prompted this reply. Mark> a traditional backup is nothing more than a strangely async Mark> raid1, with the same space inefficiency. tape is not the Mark> answer, and getting more not. the idea of a periodic snapshot Mark> to media which is located apart and not under the same load as Mark> the primary copy is a good one, but not cheap or easy. backups Mark> are also often file-based, which is handy but orthogonal to Mark> being raid (or incremental, for that matter). and backups don't Mark> mean you can avoid the cold calculation of how much reliability Mark> you want to buy. _that_ is how you should choose your storage Mark> architecture... You again mixing up your ideas here. This is the first time I've ever heard someone imply that backups to tape are a form of RAID, never. You really have an interesting point of view here. Now maybe you do have some good points, but they're certainly not articulated clearly. Just to work through them: First, backups to tape may not be cheap or easy, especially with the rise of 250gb disks for $100. Buying a tape drive that has the space and performance to backup that amount of data can be a big investment. Second, reliability is a different measure from that of data retention. I can have the most reliable RAID system on a server which can handle multiple devices failing (because they weren't reliable), or power supply failure or connectivity failures, etc. But if a user deletes a file and it can't be recovered from your RAID system, then how much help has that RAID system been? Now you may argue that reliability includes backups, but that's just wrong. Reliability is a measure of the media/sub-system. It's not a measure of how good your backups are. So you then claim that snapshots are a great way to get cheap and easy backups, especially when you have reliable RAID. So what happens when your building burns down? Or even just your house? (As an aside, while I do backups at home, I don't take them offsite in case of fire. Shame on me, and I'm a SysAdmin by profession!) So how do you know that your snapshots are reliable? Are they filesystem based? Are they volume based? If volume based, how do you get the filesystem in a quiescent state to make sure there's no corruption when you make the snapshot? It's not a trivial problem. And even traditional backups to tape have this issue. I'd write more, but I'm busy with other stuff and I wanted to hear your justifications in more detail before I bothered spending the time to refute them. John - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
