[lvm-devel] [PATCH 0 of 13] LVM add 'mirrored' log type

[Jonathan Brassow]

I've fixed the segfaults Taka reported.  I've also begun to go through
and fix the remaining issues with handling device failures in the
various different scenarios.  I could use some help testing all the
different variations.  I've described below some of the different
permutations that will now exist.  I will be going through and testing
these as well.

Device failure handling policies:
=================================
The following policies are available for both mirror logs and mirror
images...
"remove" (rm):
Take out the failed device from the LV and do nothing else.  IOW, just
make things consistent again.

"replace" (rp):
Remove the failed device and attempt to replace it with available space
in the VG.  IOW, try to recreate what was lost.

Device failure scenarios:
=========================
"2devs":
You will have to use '--alloc anywhere' to get the mirrored log to be
placed on the same devices as the mirror images.  Failing a single
device will result in a failure of an image in the mirrored log and the
mirror itself - simultaneously.  Obviously, a "replace" policy will
fail, but the results should be the same as "remove".  The final result
should be a linear device.

"3devs":
'--alloc anywhere' is still necessary.  Failing a single leg can affect
the mirror, its mirrored log, or both.  The "remove" policy can leave a
lone linear LV or a mirror with a linear log.  The "replace" policy
should be able to restore the LV.  It is also possible to test 3-way
mirrors and fail one of the legs - presumably leaving a 2-way mirror and
a mirrored log.

"5devs":
Gives the ability to have the mirrored log on separate devices from the
mirror images and be able to "replace" the device.

So, the it is necessary to test all of the fault scenarios in each cell
of the following matrix.  Any help would be most welcome.

          | 2devs | 3devs | 5devs |
----------|-------|-------|-------|
rm_l,rm_i |       |       |       |
rm_l,rp_i |       |       |       |
rp_l,rm_i |       |       |       |
rp_l,rp_i |       |       |       |
-----------------------------------

 brassow