AIX mount point question


We have produciton site and DR site, we have done the hardware copy or SAN copy for our drives.  We have the same data as Prod.

When it copied mount also creaed on DR server.  Noramlly Mount point is local to the server and disk doesn't keep mount point information.

Is some thing new on AIX compare to other unix flavours?
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If the share is not mounted the underlying "mount point" is nothing else than a regular JFS(2) directory.
Moreover, this directory is required, otherwise a subsequent NFS mount will fail.

So, if you copy all or part of a filesystem from one server to the other all affected directories are also copied.

What you saw as "mount" is just a directory (which can become a mount point later, of course).

As far as I know there's no difference between AIX and all other Unix/Linux flavors in that aspect.
mokkanAuthor Commented:
Data was copied in SAN level  ( Hard ware level),   You use the same VG name  as PROD and  you can export the VG and you can see the logical volumes,  but disk should contain  mount point info as well ?
Or mount point info local to the OS and need to create the mount locallly and mount the volumes?
The mount point is just a directory.
Such a directory is part of the filesystem just as any other directory like "/etc".
A directory (intended to become a mount point or not) is "local" to the OS, of course.

The "mount point info" is (better: can be) contained in the local /etc/filesystems file,
where the server is defined as "nodename" and the NFS options are defined as "options"
under the appropriate mount point stanza.
Such an entry is not mandatory. You can always mount a share "by hand" without an entry in /etc/filesystems.
This is very similar to /etc/fstab in Linux, yet the format is somewhat different.
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mokkanAuthor Commented:
I totally understand, it is just a directory.  Does volume group keep mount point information and store it in disk ?  Basically VGDA contains mount info?
No, everything is in /etc/filesystems, local mounts (for logical volumes) as well as (possibly) remote mounts (e.g. for NFS shares).

The VGDA holds logical volume information, but no information where and when (auto/noauto) those volumes should be mounted.

The LVCB (logical volume control block), on the other hand, does have mount point info ("label").
This label is used along with other filesystem info contained in the LVCB by "importvg"
to recreate /etc/filesystems (and to define the mount point directories, by the way).
The label ("mount point") can be overridden by a manually issued "mount" command, however,
and it can persistently be changed with "chfs -m".
"chfs" changes the LVCB as well as /etc/filesystems.
If you're interested: You can display all VGDA and LVCB info contained on a given disk "hdiskX" with:

readvgda hdiskX

Quite a lot of output, right?
mokkanAuthor Commented:
Thank  you very much. This is what I want to know, basically LVCB keeps the mount point info and when we import the  VG,  /etc/filesystems get updated, and then mount? Am  I right?  This features for only AIX right ?
You're right, importvg reads the VGDA and the LVCBs, updates the ODM with the new hdisk/LV information,
updates /etc/filesystems with the new FS information and creates the required mount points if they're missing..
The imported volume group is automatically varied on (unless the volume group is Concurrent Capable),
but the filesystems are not automatically mounted!
You will have to run "mount -a" to mount all filesystems including  the imported ones which carry the "mount=true" flag,  
and an explicit mount command is required for all imported filesystems which have "mount=false".

I didn't mention all this in my first comments because you never said that you used importvg.
I assumed we were talking about NFS mount points!

The said feature is not unique to AIX, yet IBM have been among the first to implement it.
VxFS has "vxdg import", Linux' and HPUX' LVM have "vgimport" and there might be others as well.

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mokkanAuthor Commented:
Thank  you.   It mease if we do vxdg import,  it will automatically update the /etc/fstab  or /etc/vfstab,  and then if there is no mount point, it will create accoring to LVCB ( For veritas voume manger, it might have own Logical Volume control block?
"vxdg import" makes accessible any data stored on the disk group,
including all disk and volume configurations.
As far as I know this includes merging the new filesystem info into fstab.

I'm not sure about the further implications of "vxdg import". Maybe this is worth a new question so a true VxFS expert can help.
mokkanAuthor Commented:
thank  you very much as usual.
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