On Tue Nov 01, 2011 at 05:32:17 -0400, Miles Fidelman wrote:
> Robin Hill wrote:
> > On Tue Nov 01, 2011 at 04:13:26 -0400, Miles Fidelman wrote:
> >
> >> David Brown wrote:
> >>> No, md RAID10 does /not/ offer more redundancy than RAID1. You are
> >>> right that md RAID10 offers more than RAID1 (or traditional RAID0 over
> >>> RAID1 sets) - but it is a convenience and performance benefit, not a
> >>> redundancy benefit. In particular, it lets you build RAID10 from any
> >>> number of disks, not just two. And it lets you stripe over all disks,
> >>> improving performance for some loads (though not /all/ loads - if you
> >>> have lots of concurrent small reads, you may be faster using plain
> >>> RAID1).
> >> wasn't suggesting that it does - just that it does things differently
> >> than normal raid 1+0 - for example, by doing mirroring and striping as a
> >> unitary operation, it works across odd number of drives - it also (I
> >> think) allows for more than 2 copies of a block (not completely clear
> >> how many copies of a block would be made if you specified a 16 drive
> >> array) - sort of what I'm wondering here
> >>
> > By default it'll make 2 copies, regardless how many devices are in the
> > array. You can specify how many copies you want though, so -n3 will give
> > you a near configuration with 3 copies, -n4 for four copies, etc.
> >
> >
> cool, so with 16 drives, and say -n6 or -n8, and a far configuration -
> that gives a pretty good level of resistance to multi-disk failures, as
> well as an entire node failure (taking out 4 drives)
>
Sorry, my mistake - it should be -p n3, or -p n4. You'll want -p f6/-p
f8 to get a far configuration though, but yes, that should give good
redundancy against a single node failure.
> which then leaves the question of whether the md driver, itself, can be
> failed over from one node to another
>
I don't see why not. You'll probably need to force assembly though, as
it's likely the devices will be slightly out-of-synch after the node
failure.
Cheers,
Robin
--
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( ' } | Robin Hill <robin@xxxxxxxxxxxxxxx> |
/ / ) | Little Jim says .... |
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