[CentOS] Re: Raid5 issues

Fri May 4 12:20:58 UTC 2007
Toby Bluhm <tkb at midwestinstruments.com>

Ruslan Sivak wrote:
> Feizhou wrote:
>> Ruslan Sivak wrote:
>>> Feizhou wrote:
>>>>> I do have a SIL3114 chipset, and I think it's supposed to be 
>>>>> supported by device mapper.  When I go to rescue mode, I see it 
>>>>> loading the driver for SIL3112, but nothing appears under 
>>>>> /dev/mapper except control.  Are there instructions somewhere on 
>>>>> getting it to use my controller's raid?
>>>> Your controller only has a bios chip. It has no raid processing 
>>>> capability at all.
>>>> You need to use mdadm. anaconda should be able to let you create to 
>>>> mirrors and then create a third array that stripes those md devices,
>>>> _______________________________________________
>>> Anaconda doesn't let me create a stripe raid set on top of a mirror 
>>> set.  And it doesn't detect it when I do it manually.
>>> Also the bios chip presents additional issues.  I believe when I 
>>> don't have a raid array set up, it won't boot at all.  When I have 
>>> it on raid10, I had trouble booting, and when I have it on 
>>> concatenation, everything works fine, until a drive is replaced.  At 
>>> that point, i have to recreate the array, as concatenation is not a 
>>> fault tolerant set, and at this point I seem to lose all my data.
>> It won't boot at all without a raid array setup? That sounds really 
>> funny.
> Actually I'm not 100% sure on this, but I think this is the case.  I 
> believe the first time I set it up as a raid10, assuming that linux 
> will just ignore it.  I installed centos by putting boot on a raid1, 
> and root on LVM over 2 raid1 sets.  I had trouble getting it to boot.
>>> Is there a way to get it to use the raid that's part of the bios chip?  
>> Repeat after me. There is no raid that is part of the bios chip. It 
>> is just a simple table.
> Yes, I know this is fakeraid, aka softraid, but I was hoping that 
> using the drivers would make it easier to support raid 10 then with 
> mdadm, which seems to be impossible to get to work with the 
> installer.  I'm not even sure why the raid10 personality is not 
> loaded, as it seems to have been part of the mdadm since version 1.7.
>>> Something about device mapper?
>> You need the fake raid driver dmraid if you are going to set up stuff 
>> in the bios. What version of centos are you trying to install? libata 
>> in Centos 5 should support this without having to resort to the ide 
>> drivers.
>> _________________________________
> I'm trying to install centos 5 - the latest.  How would I go about 
> using dmraid and/or libata?  The installer picks up the drives as 
> individual drives.  There is a drive on the silicon image website, but 
> it's for RHEL4, and I couldn't get it to work.  I'm open to using md 
> for raid, or even LVM, if it supports it.  I just want to be able to 
> use raid10, as I can't trust raid5 anymore.

IIRC you had two out of four new disks die? So maybe it would be more 
accurate to say it's your hardware you don't trust. Raid5 is used 
without problems by ( I assume ) many, many people, myself included. You 
could have a raid10 and still lose the whole array if two disks that in 
the same mirror die at once. I guess no software in the world can really 
overcome bad hardware. That's why we do backups :)

Anyway, perhaps excersizing /stressing the disks for a few days without 
error would make you feel more confident about the HDs.

Toby Bluhm
Midwest Instruments Inc.
30825 Aurora Road Suite 100
Solon Ohio 44139