>> This is not the same as a backup.
>>
>> RAID will protect you from physical failure of a single drive. It will
>> not protect you if you accidentally delete a file, or if some virus
>> infects your PC and deletes your stuff, or if the filesystem becomes
>> corrupted somehow, or...
> 
> It depends a lot on what you're trying to protect yourself from.

Yes, yes it does.

For the average home user, if your house burns down, you're not going to 
give a **** about the holiday photos and the copy of Nero you just lost 
- YOU HAVE NOWHERE TO LIVE!! But for a business user, losing the 
building is nothing; you can *buy* another one. But losing data = you 
will be liquidated.

> There's 
> nothing, though, that says you can't create a mirrored set, let the 
> drives mirror, and then "break the mirror" and take one drive offline.  
> I've known people who have done that and used that for disaster recovery 
> when upgrading systems.

This is a very, very dumb way to do backup. A file-level copy will be 
drastically faster. (It doesn't involve mirroring all the useless empty 
sectors.) IME, mirroring a disk typically takes something like 10 hours, 
regardless of capacity. (Lower-capacity drives are usually 
correspondingly slower too.)

Also, if you do a file-level copy, you have options such as compressing 
the data and putting multiple backups on a single backup harddisk, doing 
differential or otherwise partial backups, and so forth.

>> An often-encountered backup strategy is to copy everything onto an
>> external USB HD and then put that somewhere. I'm not sure that all this
>> turning the drive on and off won't just wear it out faster.
> 
> See my anecdotal evidence in reply to Stefan.  Two identical units, one 
> powered on and off regularly, one that was left on 24x7.  Guess which one 
> failed?  Not the one that has been turned on and off regularly for 5 
> years now.  The one that was plugged in and running for 3 years solid.

In theory, until the disks are spinning at full speed, you don't get 
that "cushion of air" for the heads to "fly" on, which should result in 
wear. Of course, no doubt manufacturers know all about this and have 
come up with ways to at least reduce the problem...

Post a reply to this message