[CentOS] Re: Duplicate PV on HW RAID?

Scott Silva ssilva at sgvwater.com
Tue Jul 29 21:38:41 UTC 2008

on 7-29-2008 2:04 PM Eduardo Grosclaude spake the following:
> On Tue, Jul 29, 2008 at 1:23 PM, Lanny Marcus 
> <lmmailinglists at gmail.com 
> <mailto:lmmailinglists at gmail.com>> wrote:
>     Eduardo: To give you something else to consider, as an alternative:  I
>     believe there was a long thread here, awhile back, about using
>     Software RAID, instead of fake RAID controllers. Software RAID works
>     very well, as I recall from reading that thread. Possibly look into
>     changing to Software RAID. Depends on the HW RAID controller.  
> Yes, I finally ended up installing software RAID because
> 1) I have read that, even if I installed the proper driver, Linux only 
> uses it to configure its own dm software RAID device according to the 
> BIOS conf-- is this completely true? If yes, no real offloading anything 
> to hardware anyway-- even under Windows; does anybody know about this 
> for sure?

Fakeraid doesn't really offload anything to hardware. Most of the drivers are 
just software raid hidden from the OS by programming "black magic". The bios 
just sets metadata or stores registers that the driver reads to know what to 
do. I believe that the linux MD raid drivers are much more robust and way more 

> 2) I am very scared by non-kernel-tree-blessed modules which have their 
> own install procedures and/or updating schedule, I have been bitten by 
> this in the past.
Join the club.
> I finally did setup two 1-RAIDed identical partitions and installed the 
> system on the rest of both disks... Now my system won't boot if one disk 
> is broken, but I hope I can go rescue into the data. I was formerly 
> hoping to rely on RAID to protect the full install and simplify my life, 
> but I was discouraged away by 1) and 2).

Follow the software raid howto and you should be able to boot from the second 
drive if the first fails.
> I have yet to see a real RAID controller... At what price do they start off?
I would guess at about $150 US (450 Argentine Pesos) for a 3ware 2 channel 
sata PCI raid card plus shipping and any local duties. Double that for 4 channels.

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