On Tue, 10 Nov 2009 10:12:57 +0000, Invisible wrote:

>> 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.

Depends on what you're trying to accomplish.  If the purpose is fast 
recovery, mirroring is a very good way to ensure you have a workable 
system if you swap the drives out.

Doing a file-level copy might be faster, but then you get to go in and 
muck about with permissions afterwards.  Mirroring takes care of all of 
that for you.

Remember - I've got decates of working with server technology behind me 
here. ;-)

>>> 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...

I would expect they do.  I used to know a guy who worked for Quantum 
years ago (I wonder what he's up to these days), and he said the 
engineering was quite impressive.

Jim

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