Re: possibly silly question (raid failover)

[Miles Fidelman <mfidelman@meetinghouse.net>]

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)

which then leaves the question of whether the md driver, itself, can be 
failed over from one node to another

Thanks!

Miles




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