Re: The Small Company's Guide to Hard Drive Failure and Linux]

[miah <jjohnson () sunrise-linux com>]

Hi Dave,

On Thu, Nov 18, 2004 at 09:49:09AM -0500, Dave Aitel wrote:
> One might think you could use dd to duplicate your drive. I initially 
> tried this, and my results were not good. I did remember to use dd 
> if=/dev/hda of=/dev/hdc conv=noerror (the noerror flag is important). 
> However, this takes forever and a day. Basically it'll take all night. 
> So be prepared for that, even on a small drive and a fast system.  They 
> sell devices that can do it faster, I think, but you don't have one, do 
> you?

Don't forget to increase the blocksize otherwise you're copying
512 bytes at a time, which will take forever. bs=1024k can speed up a
dd disk imaging.  It'll still take a while though.

> The other issue with dd is that typically replaces every sector on the 
> disk. So you'll need a disk EXACTLY the same size as the previous disk. 
> My disk was one meg smaller (40.0 Meg instead of 40.9 Meg). This was an 
> annoying problem.
>
> So instead of that, one nice option is just to get your new drive, make 
> the partitions manually with fdisk on it to replicate the original 
> drive, and then use tar to copy the contents across. I used knoppix 
> heavily here.
   
LVM could be good then.  You can do snapshots, and you can migrate
groups to new servers/disks easily.  It also supports hot-resizing of
volumes (depends on filesystem support), you can also easily add space
to your volume groups, and do raid ontop of them as well.

> The next step after doing all this is typically to make a plan that 
> involves not having to ever do this again. For those of you not in the 
> know - you want a hardware supported (get a good modern motherboard) 
> RAID-1 solution and you want to be able to swap out one of your two 
> drives (mirrored) when Linux tells you that one is bad. You also want to 
> have some sort of backup solution running (of course), and you want to 
> have a secondary DNS server and a backup machine somewhere in another 
> state (or country) that can take over if your main CO-LO goes under or 
> something. Something that can provide basic mail and web services is 
> nice. It might be good to hire an admin who is not you.
>   

Be careful here.  Some ide hardware raid implementations are not really
hardware raid at all, but a software/bios raid that relys on drivers.
Linux has had built in software raid for a while, thats usually faster
than the ide hardware raid, and its supported very well.


-miah

http://www.linuxmafia.com/faq/Hardware/sata.html#fakeraid
http://www.tldp.org/HOWTO/LVM-HOWTO/index.html
http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html
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