[CentOS] "multi-boot" drive partitioning

Tue Dec 18 05:32:37 UTC 2007
redhat at mckerrs.net <redhat at mckerrs.net>


----- Original Message ----- 
From: "Frank Cox" <theatre at sasktel.net> 
To: centos at centos.org 
Sent: Tuesday, December 18, 2007 2:55:49 PM (GMT+1000) Australia/Brisbane 
Subject: Re: [CentOS] "multi-boot" drive partitioning 

On Tue, 18 Dec 2007 14:48:57 +1000 (EST) 
"redhat at mckerrs.net" <redhat at mckerrs.net> wrote: 

> I don't understand what you are trying to achieve. Some sort of (poor mans) redundancy at the hard disk level 

A spare computer that can be swapped in to replace any of 4 other computers 
without requiring a lot of setup between "the main machine died" and "the 
spare is now online." 

? When would the "webserver quit" ? E.g. if your 
motherboard dies then it doesn't matter how many copies of an os you have 
spread over how many disks, the whole thing is unavailable. 

That's when you whip out the spare computer, plug it into the network, boot it 
up and hit "1" to load the webserver, and then take the main webserver machine 
apart and find out why it died at your leisure. At least, that's the idea. 

> Why not mirror the two 300gb drives, using software raid and install the centos virtualization and run any number of vms *all the time* ? 

Because the spare machine may have to replace any of 4 different computers that 
live on two separate networks. There is no need to have a second webserver 
running, for example, until the main webserver quits. If it quits, it would be 
nice to have another one all set up and ready to plug in. Boot up, restore the 
webpage data from last night's backup, and put it online. I want to have 
Apache set up and everything else on the spare machine before the problem 
arises. 

Same for the fileserver, the LTSP server, and so on. One spare machine that 
has 4 "personalities", as required. 

-- 
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Ahaaaaa....... 

now I get it. 

You have another computer, which, I presume, is exactly the same as the 'live' one ? 

I'd still bet my money on the the fact that you'd spend more time rooting around with installation, backups and restores than if you setup software mirroring and used virtualization. Picture this; 

1) install centos 5.1 including virtualization on mirrored 300gb hdds 
2) install any number of vms 
3a) server dies due to faulty component - remove both hdds and place in second server boot up and all vms will be running 
3b) hard drive in server fails - do nothing as it is mirrored 

I reckon step 3a could be done comfortably in under 15 minutes. 

How does this compare to your solution with regards to complexity and system availability ? 

Also, once you were happy with the virtualization setup you could run both of your machines in a 2 node cluster and have little no or downtime when hardware fails. 

Cheers. 

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