Re: How to grow RAID1 mirror on top of LVM?

[Lars Täuber <taeuber@xxxxxxx>]

Hallo David!

"David Lethe" <david@xxxxxxxxxxxx> schrieb:
> Lars:
> Even if you *could* do this, then your design would still be an awful idea.  You'd effectively have a random I/O filesystem.  Any write on a RAID1 disk would generate writes on all of the other disks.  Even with a small number of RAID1 targets and default journaling, I wouldn't be surprised if a single application write translated into at least a dozen physical disk writes.  
> 
> What if (when) both the RAID1 & RAID6 became corrupted?  How would you proceed?  How would you propose the md engine deal with this?   What if you lose a disk on the RAID6 while expanding the LVM and have a bad sector on remaining disks, or fsck shows filesytem corruption while you are expanding a md volume. 
> 
> Maybe you are starting to get the point.

No, sorry. I really don't understand. But maybe because I didn't tell detailed enough what our systems looks like.

We have here two huge RAID6 systems, that are connected through a 10G Ethernet switch. They are equally in size.
On these RAID6 we create LVs euqally in size and want them to be parts of a RAID1:

 RAID6    RAID6
monosan  duosan
  LV       LV             (multiple of)
    \     /     10GE
     RAID1
       |        10GE
      aoe
       |        1GE
     server               (multiple of)

>  What is preventing the md layer from doing what you want is that a heck of a lot of code would have to be written,

But could you tell me what in the current »design« prevents us to resize the LVs and the RAID1 on top?
When I understand it correctly the RAID information are written at the end of each accessible partition/LV.
What is different on an extended LV from a partition that is replaced with a bigger one?

[...]
Thanks
Lars

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