3-way RAID 1+0 cons...
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3-way RAID 1+0 considerations?

Eminent Member Customer

Currently I have a 1+0 using 8 disks in 2 4-bay enclosures. I'm considering expanding to 3 enclosures, and thus 3 mirrors for the RAID. My intent would be to rotate a mirror set to offsite storage. This gives me 3 questions

1 -- with one of the 3 mirrors disconnected will SoftRAID continuously show the RAID to be degraded even though 2 mirrors remain?

2 -- One of my goals with this is to take advantage of fast-rebuild. At rotation time I would move a fresh mirror offsite, leaving a single current mirror onsite, and return the old mirror to its enclosure for rebuild. Would fast-rebuild then work to update the returned mirror with all of the changes that had occurred since its removal?

3 -- I assume there must be some sort of journal mechanism to keep track of the fast-rebuild updates so they can be applied. How much space does this take and is there a way for me to view the size of this journal? I need some way to evaluate how this would affect the frequency of my mirror rotation.

currently on SoftRAID 5.6.3

Thanks for your help

Topic starter Posted : 26/09/2017 11:16 am
Member Admin

This is a question I cannot answer at this time.

We do not have the use case you require built into SoftRAID, but it is something that will be available in SoftRAID 6. that is all i can say at this time.

A 3 enclosure RAID 1+0 is 12 disks, 6 primary, 6 secondary disks. What you are asking for is 3 Primary disks and 6 secondary disks, essentially.

To start to address your other questions:
In your current case, you can remove the two secondary disks, and the volume will remain mountable, but not have any redundancy.
Any disk can fail, and the volume is mountable.
If any two disks fail from opposing sets, the volume is mountable.
Only if two disks from the same mirror pair fail is the volume not mountable.

Fast Mirror Rebuilds is an automatic process and not to worry about. It takes up no volume space and whenever you reconnect a mirror, it will discover what parts of the disk are not in sync and rebuild those. This reduces rebuild times dramatically. There is no user interaction (or investigation) needed.

Hope this helps, even though I cannot address your specific question.

Posted : 26/09/2017 3:56 pm
Eminent Member Customer

Hope this helps, even though I cannot address your specific question.

Yes, very helpful. I think I can wait for version 6, and it's good to know that the fast rebuild functionality is not limited in the way I was concerned about.

Topic starter Posted : 26/09/2017 7:06 pm