RE: [Evms-devel] EVMS and Drive Linking

[Don M. <dlm...@us...>]

>Hello Kevin, I am running tests now. Already come to a puzzle.

>Have a drive link called "ld" with 3x2gb disks, removed the middle (nr.
>2 disk) for test. Now the volume reports "ld-missing_child_1", and if I

When the drivlink plug-in fails to locate all its child link objects ... it
still needs to construct the drivelink and so it fills in the missing links
with place holders ... named xxx-missing_child_N.  The place holder object
provides a DM error mapping for its region of the drivelink so that you can
access the remainder of the drivelink.

>right click the "ld" feature object I get the Replace... option. Now, if
>I choose the Replace.. then I can replace the DriveLink with a drive.
>This seems to copy all the data from the Feature Object directly to the
>new disk.

The storage for the drivelink is replaced using an available storage
object.  You can look under the available objects tab for candidates.  Its
possible to have regions or partitions or even another drivelink storage
object that's suitable but it seems in your case that you must have had a
disk object in the avail object list that was sufficiently large for the
replace and others just were not suitable.

>What I want to do is to replace the disk in the feature object, or just

If you had a backup from the missing disk that you could restore to a
replacement disk ... then you could just run evms_activate and it would
build the drivelink with all 3 disks.  Drivelink isn't software raid ... it
can't resync.

>rebuild with the 2 existing objects and just remove the "missing_child".

You removed the middle disk ... this is a hole in the middle of your
drivelink object.  It really makes no sense to rebuild with your 2 existing
objects ... UNLESS ... you first shrink the drivelink.  If the file system
allows you to shrink down to the very first object in the link then your
home free!  Just shrink the drivelink down to the 1st disk and follow the
shrink with an expand that would pick up the disk you just freed by
shrinking ... moving the 3rd disk down to the 2nd disk spot.

>Right clicking the "ld-missing_child_1" does not present a "Replace..."
>option.

I think you realize at this point that ld-missing_child_1 is not an area on
any disk in your system.  It is simply a place holder that provides a DM
error mapping ...  so that the drivelink can be constructed and recoverd by
restoring the missing object or by shrinking the drivelink.  It makes no
sense for you to replace the missing object ... it means that your going to
find an available object and then copy the contents of ld-missing_child_1
to the object ... only the i/o is going to fail during the copy because
there is not storage backing the missing child.

-Don