On Mon, 09 Nov 2009 09:42:27 +0000, Invisible wrote:

>>> I don't know, man... Backing up spinning disk to... spinning disk? Is
>>> that such a sensible idea?
>> 
>> Mirroring (or duplexing) provides a pretty good degree of data
>> protection because the odds of both drives dying at the same time are
>> pretty small.
>> 
>> It's been used for a very long time.
> 
> 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.  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.

>> But I also back up directories from several systems to other systems
>> using rsync.
> 
> Now that's more like it.
> 
>> Well, I didn't say anything about shutting the drive down.
> 
> 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.

> PS. I've yet to find a consumer RAID controller which actually works
> properly. They all seem to be hopelessly unreliable. And most of them
> are software RAID anyway; the controller is a normal IDE or SATA
> controller, and the Windows driver does all the actual RAID functions in
> software. It seems that only the £££ server-grade controllers actually
> do the job properly.

Software raid exists for some platforms - and for mirroring for backup 
purposes, that's really all you need.  Heck, you could do it over iSCSI 
with a fast enough connection (I've seen that done as well).

Jim

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