Backup with dd?

[Andrew P.]

Eric F Crist wrote:
> On Jan 3, 2005, at 12:15 PM, Henry Miller wrote:
> 
>>
>> This might work, but it isn't best.   I can think of the following
>> objections:
>>
>> You have no protection at all while the copy is in progress.  You have
>> overwritten part of the old backup, but not enough to be consistent.
>>
>> You have made no provision for data loss because of anything other than
>> a failing drive.   If your house burns down you can't get your data.
>> (not strictly true, you can recover accidently deleted files so long as
>> you do the undelete before the next time you do the backup)
>>
>> FreeBSD has a few different RAID options.   With the right setup you
>> can achieve disk reliability, and not have to switch cables on reboot.
> 
> You seem to be under the impression that I'm doing this for the sole 
> reason of a disk crash.  I'm actually doing it for more than just that 
> reason.  For example, if my system gets hacked, most hackers will 
> probably not care about an unmounted hard drive, and screw with the 
> current mounted partitions.  Also, these drives wouldn't really be at 
> the same point of this hypothetical drive failure, since one hard drive 
> will only be used roughly once a week, while the other is in a constant 
> state of use.  Most of my user-data is destined for a RAID-5 array 
> that's roughly 1.2TB, so that's got it's own backup.  This is simply for 
> use in an emergency, so I don't HAVE to rebuild.  Quite frankly, I don't 
> have time to sit here and rebuild this system again any time soon.  This 
> configuration I'm trying is ideal, with minimal interference.  I'm going 
> to be installing removable drive bays so that my roommate is able to 
> simple swap drive positions and reboot the system (it's headless, and 
> he's not very tech savvy in this regard).
> 

Backing up with dd is ultimately straightforward, but is not a good
idea at all. The matter is when dd is running, the source may be
modified and the copy might be inconsistent. Software RAID should be
the best option for your task: you can mirror a drive to a second one
and then just plug the second one out of your computer.

Best wishes,
Andrew P.