[H-GEN] Cloning Linux System

[Robert Brockway]

On Sat, 4 Jun 2005, Kelvin Heng wrote:

> I need to clone a Redhat Linux (7.2) server to a secondary location 
> (e.g. Another Server or USB HDD). But I have some restriction, I am not 
> able to have any downtime for the server and will be required to carry 
> out this task while the system is operational.

This is an interesting problem - not being able to have any downtime.  

All systems will need some downtime eventually.  At the very least they'll 
need a reboot to upgrade the kernel or make sure an old vulnerable library 
is completely gone, but a hardware fault will get them at some stage if 
they run long enough[1].

If a system is so integral that you need its services all the time then it 
has to be in some sort of hot swap, cluster or fail over situation.  The 
best a serious high availability environment can really offer is 6 
sigma[2] and this costs a lot of money.  Mucho $$$$.

Basically if the company is telling you that scheduled downtime (even in 
an inconvenient window like 4am-5am) is not an option then they have a 
serious problem that will come back to bite them one day.

> Please advise if you know of any method. Thanks in advance.

There are many ways to do this under *nix.  A method using tar is 
described here:

http://www.opentrend.net/movingfilesystems.sht

I've actually seen different versions of tar respond a bit differently to 
some of those switches so if you try this method and see a problem, reply 
to this email and we can look at it.

SGI strongly recommends xfsdump/xfsrestore if you are using their xfs 
filesystem.

Sorry this has wandered off your desired topic :)

[1] Just tonight I had to take down one of our boxes with serious 
filesystem errors.  It turned out an IDE cable had shaken slightly loose 
and trashed / and /usr.  This is not a particularly important box so no 
mirroring or anything.  My first thought was a dying disk as one of the 
drives was getting on.  After rebooting from a rescue CD both drives had 
disappeared - they were not even detected by the BIOS.  I powered the box 
down and opened it up. When I pressed the IDE cable back in I did not 
notice it move but the drives got detected on the next powerup so that 
seems to have been the issue.  I'm currently running badblocks on the 
drive that had the failures (just in case) and then I'll do a full restore 
from our backups[3].

[2] Failure is 6 std deviations above the mean.  IIRC this is 5 minutes 
downtime per year.

[3] The value of a proper disaster recovery plan cannot be overstated.

Rob

-- 
Robert Brockway B.Sc.
Senior Technical Consultant, OpenTrend Solutions Ltd.
Phone: +1-416-669-3073 Email: rbrockway at opentrend.net http://www.opentrend.net
OpenTrend Solutions: Reliable, secure solutions to real world problems.
Contributing Member of Software in the Public Interest (http://www.spi-inc.org)