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Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"?



On Mon, Apr 13, 2009 at 5:55 PM, Bryn M. Reeves <bmr redhat com> wrote:
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> John Hughes wrote:
>> malahal us ibm com wrote:
>>> John Hughes [john Calva COM] wrote:
>>>
>>>> John Hughes wrote:
>>>>
>>>>>                if (lp->stripes > 1) {
>>>>>                        log_error("mirrors and stripes are currently "
>>>>>                                  "incompatible");
>>>>>                        return 0;
>>>>>                }
>>>>>
>>>>> Should I just stick with mdadm for my mirroring and striping needs?
>>>>>
>>>
>>> You can do it today with some hassle or wait until someone implements a
>>> feature called 'generic layering'. The feature really means, treat some
>>> LVs as PVs!
>>>
>>> How can you do raid10 today? Create two raid0 LVs. Lets us call these
>>> lvgroup0/lv0 and lvgroup0/lv1. Now create raid1 lv in lvgroup1 where
>>> lvgroup1's PVs are lvgroup0/lv0 and lvgroup0/lv1.
>>>
>>> Isn't that a rai10 volume?
>
> No, it's a RAID 0+1 (RAID01/mirror of stripes).
>
>> To increase the chances of surviving a double-disk failure it would be
>> better to raid-0 a bunch of raid-1's.
>
> This is RAID1+0 (RAID10/stripe of mirrors) - it's usually preferable to
> 0+1 not only because of the improved redundancy but also the individual

I disagree.

Look at this:
http://www.pcguide.com/ref/hdd/perf/raid/levels/multXY-c.html

> mirror sets can have failures and recover independently. When a strip
> set in a RAID0+1 fails the entire mirror must be re-synchronised giving
> longer recovery times and more performance degradation during the rebuild.
>



>> Are we sure there are no deadlock problems with LVM2 layered on top of
>> LVM2?
>
> Stacked volumes work fine, there's just limited support in the tools for
> creating them without going to a lot of manual effort at the moment.
>
> Regards,
> Bryn.
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>



-- 
Regards,
Sandeep.





 	
“To learn is to change. Education is a process that changes the learner.”


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