IDS Forum

Re: Using VMotion to move informix server

Posted By: Art Kagel
Date: Tuesday, 11 June 2013, at 11:54 a.m.

In Response To: Using VMotion to move informix server (S M MAHESH)

The problem is likely that Informix does not initialize the unused portions
of RAW disk chunks that it uses so the unused portion of each RAW chunk is
most likely filled with binary zeroes. The VMotion utility is assuming
normal file behavior and truncating the NULL portion of the chunks when it
creates the mapped files in the VM. Informix tries to write a new page to
what it thinks is an already allocated fixed length file or a certain size
and finds that it gets an EOF error because VMotion truncated the file.
Keep in mind that these kind of physical level disk copies an only be
successfully performed on Informix chunks with the engine either completely
offline or in a blocked state (onmode -c BLOCK)! Here's what you have to
do:

1. Use dd to look at the last "page" of each chunk. If that page is all

NULLs then

- Use dd to write anything to that last page. Since Informix expects

that it contains garbage it will overwrite whatever you put there when it

finally needs to use that space.

2. If it contains data, then LEAVE IT ALONE, this chunk will be OK!

Example: (SEE THE WARNING AT THE END OF THIS RESPONSE BEFORE DOING
ANYTHING!)
Say you have a chunk that contains 100,000 2K pages, so its size in onstat
-d is 100000, check the last page with:

dd if=/my/chunk/path bs=2k count=1 skip=99999 2>/dev/null | sum

If the page is empty (ie nulls) then the output from sum will look like:
00000 2

The zero checksum is only possible if the page contains no data except
zeros, not even garbage. If you get a non-zero checksum, you may want to
make sure that the page doesn't contain some data but still ends in zero
bytes by piping it to "od -x" instead. Chunks like this should be patched
as well.

Then overwrite the last page:

ls -l | dd of=/my/chunk/path bs=2k count=1 seek=99999

WARNING - DO NOT DO THIS WITH A FILESYSTEM CHUNK because dd will truncate
the file destroying your data when it opens it for writing YOU CAN ONLY DO
THIS SAFELY FOR A RAW DEVICE BASED CHUNK!!!!!!!!!!!!!!

BEFORE YOU DO ANYTHING LIKE THIS, make sure that you have a viable archive
of the server in hand that's been tested with archecker or by trying to
restore it to another machine.

Art

Art S. Kagel
Advanced DataTools (www.advancedatatools.com)
Blog: http://informix-myview.blogspot.com/

Disclaimer: Please keep in mind that my own opinions are my own opinions
and do not reflect on my employer, Advanced DataTools, the IIUG, nor any
other organization with which I am associated either explicitly,
implicitly, or by inference. Neither do those opinions reflect those of
other individuals affiliated with any entity with which I am affiliated nor
those of the entities themselves.

On Tue, Jun 11, 2013 at 11:14 AM, S M MAHESH <smahesh@cisco.com> wrote:

> Hi folks,
>
> We are trying to use VMWare VMotion software to do a physical to virtual
> machine conversion of a box running Informix. Vmotion is a converter tool
> that
> can be used to convert a physical machine to a virtual machine running on
> VM
> ESXi server. We are seeing issues with the dbspace files after converting
> the
> physical box to a virtual one. The dbspace files for one of the chunks is
> running out of disk space (free size is zero post migration).
>
> The suspicion is that the VMotion tool does not understand the internal
> formats of the dbspaces files. VMotion has issues with "raw disk" files.
>
> * Has anyone successfully migrated their Informix servers from a physical
> server to ESXi 5.0 VM server using the VMotion tool?
>
> * Has anyone seen the "dbspace running out of disk space" issue when
> migrating
> from physical to virtual machine? If so, how did you resolve it?
>
> * What could cause the dbspaces size to grow? Is the size tied to disk
> layout
> of the file?
>
> * Is there any way (any tool/scripts?) to compact/repack the dbspaces to
> the
> original size?
>
> Right now, other than the database, the rest of the system is working fine.
> Only the database is problematic because dbspaces reports free size as
> zero.
>
> Any suggestions/hints/solutions to troubleshoot/resolve the problem will be
> helpful.
>
> Regards,
> Mahesh
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--089e013d192005d37604dee2ea16

Messages In This Thread

• Using VMotion to move informix server
  S M MAHESH -- Tuesday, 11 June 2013, at 11:14 a.m.
  • Re: Using VMotion to move informix server
    Art Kagel -- Tuesday, 11 June 2013, at 11:54 a.m.
    • Re: Using VMotion to move informix server
      Paul Watson -- Tuesday, 11 June 2013, at 12:07 p.m.
    • Re: Using VMotion to move informix server
      S M MAHESH -- Tuesday, 11 June 2013, at 12:19 p.m.
      • Re: Using VMotion to move informix server
        Art Kagel -- Tuesday, 11 June 2013, at 12:27 p.m.

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