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When to create a software RAID array in Ubuntu

Posted on 2011-03-09
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Last Modified: 2012-05-11
Hey there,

I'm setting up a software raid using Ubuntu Desktop and wondered if it's better to create the array during the initial installation or after I've installed the OS?

Thanks!
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Question by:ttist25
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by:Iekos
Iekos earned 1000 total points
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Create the Raid before OS is better in my opinion so if you choose, Ubuntu can also be on Raid.
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by:4runnerfun
ID: 35083333
Also, if you're going to create it before OS install, you'll need the Alternate install CD/DVD. You'll then be able to setup the drives/partitions. The standard install doesn't give the option from what I recall.
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David earned 1000 total points
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Nothing more to add to above, except that this is probably the only opportunity you have to actually test to see if it works.   So I would make a dry run and install, but just take defaults and don't spend time setting up anything that takes more than a few seconds of your time and let it run.

Make sure BOTH disks are in the BIOS boot path.

After installed, power off.  Open up the case of the PC and locate all cabling, find out where the POWER is to the primary boot disk and move cabling around and get it loose so you can unplug it safely while system is powered up.  If you have a case power kill button, tape it over so the system runs with case open.

Then boot & log in.   Do something that requires I/O,   like dd if=/dev/md0 of=/dev/null &
this reads from the raid array into boot bucket

Then carefully unplug power to the primary boot disk.
If you did it right the system will stay booted and the dd command will continue to run.

If successful, then just power it off, plug everything in, close the case, and re-install, and then you can sleep at night knowing RAID1 is working!

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by:David
ID: 35083527
P.S.  after you power it off, but before you plug in the disk, then reboot. This insures system boots ok when it is degraded.    Power off, and then plug in the primary boot disk.   Then power on, then it *should* actually boot from the secondary disk, and then you can practice repairing the degraded RAID1.  Might as well have a dry run through repair as well, so you know how to do it.   Some day you'll be thankful you did :)
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by:ttist25
ID: 35084959
Ok - dry run is a great idea.  Create the array first - got it.  I just downloaded the Alternate ISO as well.

My mobo doesn't support RAID (it's a Dell Poweredge T110) and I'm using three 500GB drives (I should've specified that initially - sorry).  I'm assuming RAID 5 will be the best way to go as 1TB is enough space for me.  

Given that, are their any differences in the dry run steps or any other recommendations you have?

Thanks for everything.  It's greatly appreciated.  
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by:4runnerfun
ID: 35085055
That should work great for you. My latest file server setup was 7 x 500GB with RAID 6. Turned an OLD LanParty desktop system into a home media server / file server.
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by:David
ID: 35085174
You really want to then partition the disks so that you split the O/S into a grub partition and make it RAID1, (but a 3-way RAID1), then put the rest on a 3-disk RAID5.  Linux will let you do that, and in fact, if your data can be organized so that the O/S can be separated from whatever you need for your applications, then personally I would make it into 3 partitions, a 3-way RAID1 for both grub & your operating system, swap, and everything else, then a RAID5 for /r5    and then your databases or whatever go there and it is raid5.


RAID5 is horrible for writes as you know, but LINUX software RAID does things like balancing reads across each disk in a RAID1, so you will get great performance.  In fact, put any write intensive and most important stuff in the RAID1 partition, so you get 3 copies for added protection!

Doing mixed RAID levels works quite well, and is advanced, and many don't even know it is possible, but plenty of examples online on how to create rather sophisticated configurations if you just google configure md raid linux
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by:ttist25
ID: 35094689
I found out that I DO have an S100 PERC controller built into the MOBO.  I spoke with a Dell rep that first told me no but the second guy pointed out that there is one.  

I'll post a new question as you guys have done more than enough on answering this one.
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by:ttist25
ID: 35100970
I have posted a new question about how to recover here in case anyone wants to give it a shot.  
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