## extend mirrored disks on SSA

### extend mirrored disks on SSA

Hi folks!
I have a logical volume over 3 physical volumes in a SSA external
enclosure mirrored over 3 other physical volumes standing in another
SSA external enclosure. I created this mirror using "exact map" option.
Next I tried to expand this logical volume, but the mirror
automatically spans over different disks without use of "exact map".
Is there someone who knows what can I do to map mirror exactly??

Gianni

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### extend mirrored disks on SSA

I'm not sure what you mean by exact map.  No such option exists to my
knowledge with the standard LVM commands.  However, I think I know
what's happening in your case (I've seen this many times).

I suspect you have set this LV's interpolicy to maximum (so that it is
spread evenly over 3 disks), and then mirrored to 3 new disks (which
you probably originally mirrored by specifying the 3 new disks by
name), so that the mirror was mapped evenly over the second set of
disks.

For example, you originally had something like this:

LP    mirror1     mirror2
1     hdisk1      hdisk4
2     hdisk2      hdisk5
3     hdisk3      hdisk6
4     hdisk1      hdisk4
5     hdisk2      hdisk5
6     hdisk3      hdisk6

Then, my guess is that you increased the LV without specifying any
disks, which has the effect of evely spreading BOTH copies over all
disks in the volume group.  I.e.:

LP    mirror1     mirror2
...
7     hdisk1      hdisk4
8     hdisk2      hdisk5
9     hdisk3      hdisk6
10    hdisk4      hdisk1
11    hdisk5      hdisk2
12    hdisk6      hdisk3

If you think carefully about the implications of what "maximum
allocation" or "maximum interpolicy" means, you'll arrive at the
conclusion that there are these basic options for extending an LV that
is set up with maximum interpolicy over a set of x disks and mirrored
the same way to a separate set of y disks:

1.  Remove the copy, increase the LV, and recreate the disks.
2.  Use a map file that specifies the PPs for the first copy followed
by the PPs for the second copy.

Kevin

> Hi folks!
> I have a logical volume over 3 physical volumes in a SSA external
> enclosure mirrored over 3 other physical volumes standing in another
> SSA external enclosure. I created this mirror using "exact map"
option.
> Next I tried to expand this logical volume, but the mirror
> automatically spans over different disks without use of "exact map".
> Is there someone who knows what can I do to map mirror exactly??

> Gianni

--
Kevin R. Gee
MS Student, University of Texas at Arlington, Arlington, TX