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Re: RAID5 + 1 extra disk HOW

roland wrote:

I have a server running on RAID5, on which I would like to add a 4th disk, with a seperated filesystem. I need to have some workspace. The same disk could be used to replace a failing disk.

This is a spare disk, and can be used only as such. I'm not sure what you had in mind by "seperated filesystem," but you can't install another drive such that Linux will use the drive in two ways at once. If that was your intent it pretty much isn't going to work, and if the spare was deployed all data on it would be lost.

Stuart Sears explaned me howto install this disk as a hot spare, but it looks to me a little bit to dangereous. This server is serving 20 workstations, so I need to do this without taking to many risks. I admit to be a novice on the matter of diskmanagement. I always do standard installation of a filesystem.

Assuming you just want to add a spare, something like this works fine:
	mdadm --add /dev/md0 /dev/sdf1
Then a cat of /proc/mdstat should show the device added, running as a spare. I did that, then failed one of the existing drives, and the array rebuilt on the spare just fine, and I got a message from monitor mode saying it happened and was fixed.

So if someone could tell me howto do this in a simple way. I searched the internet for a simple howto, but was unsuccessful. I have to do this at a client in France, few hours driving

Could someone keep me from having a sleepless night?

I would test the existing array before counting on it to be okay, just in case a bad spot developed.See the wiki (http://linux-raid.osdl.org). Oh, and there is a linux-raid mailing list where there are lots of us who have found problems the hard way and want to share.

Bill Davidsen <davidsen tmr com>
  "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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