Ubuntu Server Hotswap RAID 1: Hardware or Software

hardware-raidraidsoftware-raidUbuntu

I'm building new servers for a project I'm working on. They will all run Ubuntu Server x64 (10.04 soon) and require a RAID 1 hotswap configuration (just two drives) to minimize downtime.

I'm not worried about Raid performance. The server hardware will have plenty of CPU power, and I'm only doing a RAID 1. My only requirements are:

Everything, including the OS, must be mirrored.
There must be no down-time when a drive fails. I need to be able to swap out the failed drive with another and have the RAID rebuild itself automatically (or maybe by running a simple script).

I'm wondering if the built-in Ubuntu Software RAID can handle this, particularly the hotswap part. 10.04 looks promising.

I'm considering buying the 3Ware 9650SE-2LP-SGL RAID controller, but with the number of servers we're purchasing, that would increase the total price quite a bit.

Any advice at all would be appreciated. Thank you.

Best Answer

I have hot swapped drives using the software RAID builtin into the Linux kernel on many occasions. You may need to run a command to add the new device. I believe it is possible to make it automatic, but in the places where I use it manually running the command to add the new drive has never been a problem.

I am not entirely certain that the computer will survive with zero downtime. That may depend on your hard drive controller and how it responds to a drive failure.

Related Solutions

RAID – Software RAID vs Hardware RAID

I prefer HW raid, 'cause if you have to pull good disks out of a dead machine you're not limited to the OS configuration of the raid "array".

You do keep backups of your RAID controllers config, don't you?

So just load that up on a donor machine, slot in the drives (in the right order! You did label your drives before your pulled them right?) and restart on a clean OS and your data is recovered.

THE OS DRIVES ARE NOT IMPORTANT DRIVES TO KEEP. THE MOST IMPORTANT STUFF TO KEEP IS THE DATA DRIVES!!!!

(You do backup your DATA drives, right?)

Ubuntu: Monitor hardware RAID and notify upon failure

3ware provides 3dm2 monitoring / management program. just look onm their webpage, there is a binary version of it for linux, and it even works fine [under debian at least].

thing is - i never trusted those fancy tools... so i do as follows. so i use own scripts based on tw_cli - also downloadable from 3ware website.

once per week i run patrol read:

./tw_cli /c0/u0 start verify

and all the time, every 15 minutes i dump current state of raid:

./tw_cli /c0 show > current.txt

i use very simple nagios plugin to check if current status is identical to expected [ i just compare content of a file to well known status dump that was taken at the beginning ].

#!/bin/bash

if [ `diff current.txt expected.txt|wc -l` -ne 0 ] ; then
        echo "CRITICAL - current state of raid does not match expected pattern "
        exit 2
fi

if [ `find . -name current.txt -mmin -16|wc -l` -ne 1 ] ; then
        echo "CRITICAL - state file is old "
        exit 2
fi
echo "OK"
exit 0

you would probably put mailing instead of exit 2... or even more probably use 3dm2.

Best Answer

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RAID – Software RAID vs Hardware RAID

Ubuntu: Monitor hardware RAID and notify upon failure

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