Re: 2 mirroring disks

 
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Konrad Hegner
Frequent Advisor

2 mirroring disks

Hi there!
Question for my knowledge: We have 1 main disk who is mirrored with 2 mirroring. Whats happen if the main-disk goes down.
How works the mirroring with the two alternate disks? Works the mirroring still with this 2 mirroring disks. (For the right understanding: the mirroring isn't split on two disk - it are two mirrorings)

And now in German:
Fuer jene, die auch Deutsch sprechen: Was passiert, wenn ich eine Disk zweimal gespiegelt habe und dann die 'Hauptdisk' abstuerzt. Wie arbeitet das 'mirroring' weiter? Arbeite nun nur noch eine Disk, oder 'spiegeln' die restlichen Beiden sich gegenseitig?

Thanks and regards Konrad
4 REPLIES 4
Michael Steele_2
Honored Contributor

Re: 2 mirroring disks

In general, there is no main disk since all can support what's been mirrored automatically and all are considered equivalent. Here is a bad mirrored disk replacement procedure:

swap out bad mirror
vgcfgrestore -n /dev/vg## /dev/rdsk/c#t#d0
vgchange -a y vg##
vgsync vg##

Really, no biggie.

The only benefit for 2 mirrors comes with hot backups, but his procedure has a fairly high degree of difficulty associated to it and is not for the weak at heart.
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Michael Steele_2
Honored Contributor

Re: 2 mirroring disks

OK... For the right understanding: the mirroring isn't split on two disk - it are two mirrorings)

When you execute lvdisplay is the allocation policy strict? If strict then two disks must be used.
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Armin Feller
Honored Contributor
Solution

Re: 2 mirroring disks

If there are 2 mirror copies (lvdisplay) and one disk fails the other 2 disk keep synchronized. Each write/read goes to all disks parallel so it doesn't metter which disk fails.
Konrad Hegner
Frequent Advisor

Re: 2 mirroring disks

OK, I had a discussion in the office. There is no 'main'. Read/write is parallel.

Armin is absolut correct with his answer.

Danke Armin