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Installing a (mirror) raid
http://forums.linhes.org/viewtopic.php?f=1&t=20862
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Author:  popatim [ Mon Feb 22, 2010 12:34 pm ]
Post subject:  Installing a (mirror) raid

Hello,
I would like to use the built in raid capabilities of my old mother board, a gigabyte ga-k8vm800m rev2, which uses the via VT8238R raid for Sata.

The raid is setup at the bios level but the install package does not load the raid drivers it seems and only detects the drives individually instead of the array. I am positive the array works (worked under XP and just had been running freenas), so I assume I just need to install drivers but this is where my linux newbness comes in. I don't really know how to load drivers or the updates for that matter.

I'm assuming I would need a 3rd drive to load the OS to so I can load the raid drivers? Could this be a usb stick as in FreeNas? I do have some small IDE drives if that would be better.

I bought 2 books on Linux but I really would like to get this going before I go on vacation in 10 day.

Thanks for your help.
Tim

Author:  Martian [ Mon Feb 22, 2010 1:14 pm ]
Post subject: 

With Linux you basically have two options when it comes to drivers: Built into the kernel or as a module. Unfortunately when it comes to RAID you end up with a chicken / egg situation when you try to load RAID drivers as a module (ie. you need to be able to read from your disk in order to load the module which allows you to read from your disk...)

Based on your report I'm guessing that driver support for your VT8238R chip is not enabled in the stock LinHES kernel which basically leaves you with three options:

1) Compile a new kernel with built in support for the VT8238R chip allowing you to boot from a RAID 1.

2) Find / compile a module (but wouldn't have to recompile the kernel) for the VT8238R and load it on bootup. This will NOT allow you to boot from a raid but will allow you to mount non-bootable (ie. storage) partitions as a RAID once the kernel is up. (for example you could have your /myth partition on a raid but not your / or /boot )

3) Use software raid! - While perhaps a little higher on the learning curve, this is probably your best option. You shouldn't need to mess with recompiling the kernel or finding raid modules (I'm pretty sure everything you need for software RAID is baked in the LinHES kernel).
Using the raid on your motherboard - if / when your motherboard dies you are stuck finding a RAID solution that uses the same VIA raid chip in order to get it back online and in some cases even read your data (Ouch!) With software raid you can bring the RAID back up on any hardware that can boot your kernel. Best of all there is no performance hit with utilizing software RAID as opposed to your on-board raid. In fact Linux software raid is often faster and less buggy than bios based motherboard implementations.

Hope this helps!

Martian

Author:  christ [ Mon Feb 22, 2010 7:31 pm ]
Post subject: 

I second the use of software raid. In addition to the above you will be able to maintain and repair a software raid from the command line. I use it for all of my arrays.

Author:  JoeF [ Mon May 31, 2010 3:29 pm ]
Post subject: 

Martian wrote:
Best of all there is no performance hit with utilizing software RAID as opposed to your on-board raid.

Hmm, I think you got that wrong.
With software RAID, at least with mirroring, there IS a performance hit, since the kernel has to write to two drives
With hardware RAID, that's done on the firmware level, in the background, avoiding the performance hit.

Author:  Martian [ Tue Jun 01, 2010 10:29 am ]
Post subject: 

JoeF wrote:
Martian wrote:
Best of all there is no performance hit with utilizing software RAID as opposed to your on-board raid.

Hmm, I think you got that wrong.
With software RAID, at least with mirroring, there IS a performance hit, since the kernel has to write to two drives
With hardware RAID, that's done on the firmware level, in the background, avoiding the performance hit.


While in theory you are correct, in practice the motherboard based SATA RAID controllers are not truly hardware based, as they have no processor or dedicated memory. Basically they just move the software (firmware technically) to a lower level. Again, in theory, this could speed things up a little bit but often times those "hardware" based solutions aren't as efficient as Linux software RAID. Linux Software RAID has been tweaked and refined for over a decade whereas those BIOS based RAID chips probably only have a few months of engineering time in them.

I know which one I'd rather trust my data to, even if the competition could (in theory) be faster.

I'm obviously bias toward software RAID, sorry if I went all fanboy on you there.

Martian

Author:  mihanson [ Tue Jun 01, 2010 1:26 pm ]
Post subject: 

As a user of software RAID, I'll chip in a vote for it as well. Here's a tutorial I use when I can't remember what I need to do. It's from 2003 but still valid. You can skip down to "Creating an Array" as installation instructions are not relevant for LinHES.

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