epike on 2 Sep 2004 23:21:01 -0000

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Re: [PLUG] Disaster Recovery Strategies

On Thu, 02 Sep 2004 11:01:29 -0400
David Richardson <dgr24@drexel.edu> wrote:

> I have a linux machine that I would like to be able to completely 
> restore to its current configuration in the event of a hard drive 
> failure.  I'd like to be able to just pop in a new hard drive, and have 
> it magically work like the old one without the need to manually install 
> or configure software.
> I was thinking about just using dd to copy the entire hard drive on the 
> currently working machine to a file and then if I ever need to put in a 
> new drive just using dd to write the contents of the old drive onto the 
> new drive.  Is it a problem if the new drive is a different size than 
> the old?  Or does anyone have a suggest of a better way?
> Thanks,
> Dave


DD: I wouldnt dd an entire disk, it could be dependent on the disk geometry
    (better make sure the disks have the exact geometry).  how about
    dd just the partitions.  

    the downside is how often do you want to dd the disk.  

software raid: I think is a good idea.  You dont even have to have the same
    disks.   For example, software raid level 1:

    80 gigs          120 gigs    size         example device
    partition1       partition1  40gigs       /dev/md0
    parition2        partition2  20gigs       /dev/md1
    partition3       partition3  20 gigs      /dev/md2
                     parition 4  swap         swap
                     partition5  60 gigs      /dev/hdg5 

    something like this is possible (in the above example
    you dont need to protect swap or hdg5, for example
    /dev/hdg5 might be /tmp).  in fact this is what i did
    on my home server till i got tired of it and reverted back
    to non-raid (long story).  or you could just put exact
    same disks and do a raid level 1 on them--note that
    software raid works with partitions (not disks).

    in the event of one drive failing, you'll need to partiton
    the replacement disk similar to the old one, probably
    configure the raid setup again (i dont remember exactly),
    and reinsert the new disk (raidhotadd, I think).  There is
    still some work to do, but fortunately your data will still
    be surviving on one or the other disk.

    if your doing software raid, and if you have IDE, its best to
    put the disks each on its own cable (master/slave for raid
    components is not recomended).  so a separate inexepensive
    ide controller is a good idea.

    This wont protect you from errors (e.g. if you delete files
    accidentaly the raid disks will do it faithfully), only
    from media failures--replace one or the other disk at
    signs of drives failing.

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