Ross Walker wrote:
> On Aug 30, 2009, at 10:33 PM, Christopher Chan <christopher.chan@xxxxxxxxxxxxxxx
> > wrote:
>
>
>>>>> How would one setup RAID 1+0 (i.e. 2x mirror'ed RAID1's and then a
>>>>> RAID 0 on top of it) on say CentOS 4.6 ?
>>>>>
>>>>>
>>>> Setup both RAID-1 arrays then stripe them with LVM?
>>>>
>>>> http://www.redhat.com/magazine/009jul05/features/lvm2/
>>>>
>>>> Though I'd prefer to opt for a hardware raid card, I think
>>>> you said you had SATA disks, which if that's the case would
>>>> go for a 3ware.
>>>>
>>>> nate
>>>>
>>>>
>>>> _______________________________________________
>>>>
>>>>
>>> Nate, this is what I was looking for :)
>>>
>>> I'm going away for 2 weeks now, but will definitely give it a shot as
>>> soon as I can,
>>>
>>>
>>>
>> I would NOT do that. You should like the md layer handle all things
>> raid
>> and let lvm do just volume management.
>>
>
> Your under the asumption that they are two different systems.
>
You're under the assumption that they are not.
> Md RAID and LVM are both interfaces to the device mapper system which
> handles the LBA translation, duplication and parity calculation.
>
Are they? Since when was md and dm the same thing? dm was added after md
had had a long presence in the linux kernel...like since linux 2.0
> I have said it before, but I'll say it again, how much I wish md RAID
> and LVM would merge to provide a single interface for creation of
> volume groups that support different RAID levels.
>
>
Good luck with that. If key Linux developers diss the zfs approach and
vouch for the multi-layer approach, I do not ever see md and dm merging.
>
>> To create a raid1+0 array, you first create the mirrors and then you
>> create a striped array that consists of the mirror devices. There is
>> another raid10 module that does its own thing with regards to
>> 'raid10',
>> is not supported by the installer and does not necessarily behave like
>> raid1+0.
>>
>
> Problem is the install program doesn't support setting up RAID10 or
> layered MD devices.
>
Oh? I have worked around it before even in the RH9 days. Just go into
the shell (Hit F2), create what you want, go back to the installer. Are
you so sure that anaconda does not support creating layered md devices?
BTW, why are you talking about md devices now? I thought you said md and
dm are the same?
> I would definitely avoid layered MD devices as it's more complicated
> to resolve disk failures.
>
Huh?
I do not see what part of 'cat /proc/mdstat' will confuse you. It will
always report which md device had a problem and it will report which
device, be they md devices (rare) or disks.
> In my tests an LVM striped across two RAID1 devices gave the exact
> same performance as a RAID10, but it gave the added benefit of
> creating LVs with varying stripe segment sizes which is great for
> varying workloads.
Now that is complicating things. Is the problem in the dm layer or in
the md layer...yada, yada
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