On 2022-11-10 at 08:40, Curt wrote: > On 2022-11-08, The Wanderer <wanderer@fastmail.fm> wrote: > >> That more general sense of "backup" as in "something that you can >> fall back on" is no less legitimate than the technical sense given >> above, and it always rubs me the wrong way to see the unconditional >> "RAID is not a backup" trotted out blindly as if that technical >> sense were the only one that could possibly be considered >> applicable, and without any acknowledgment of the limited sense of >> "backup" which is being used in that statement. > > Maybe it's a question of intent more than anything else. I thought > RAID was intended for a server scenario where if a disk fails, you're > down time is virtually null, whereas as a backup is intended to > prevent data loss. If the disk fails, the data stored on the disk is lost (short of forensic-style data recovery, anyway), so anything that ensures that that data is still available serves to prevent data loss. RAID ensures that the data is still available even if the single disk fails, so it qualifies under that criterion. > RAID isn't ideal for the latter because it doesn't ship the saved > data off-site from the original data (or maybe a RAID array is > conceivable over a network and a distance?). Shipping the data off-site is helpful to protect against most possible causes for data loss, such as damage to or theft of the on-site equipment. (Or, for that matter, accidental deletion of the live data.) It's not necessary to protect against some causes, however, such as failure of a local disk. For that cause, RAID fulfills the purpose just fine. RAID does not protect against most of those other scenarios, however, so there's certainly still a role for - and a reason to recommend! - off-site backup. It's just that the existence of those options does not mean RAID does not have a role to play in avoiding data loss, and thereby a valid sense in which it can be considered to provide something to fall back on, which is the approximate root meaning of the nontechnical sense of "backup". -- The Wanderer The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man. -- George Bernard Shaw
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