re[2]: Heartbeat with dual SCSI config

[Greg Freemyer]

I've used Compaq's LVM to create logical disk groups that by definition can 
only be owned by one server at a time.  (I think that Compaq's LVM is actually 
just a re-labelled Veritas LVM, and that the Veritas LVM was the conceptual 
basis for Sistina's LVM.)

Does anyone know if the Sistina LVM for Linux support this feature?

Note: I would still recommend the Stonith device.  At least with the Compaq 
LVM, there are ownership override commands you have to issue on a non-graceful 
failover.

Greg Freemyer
Internet Engineer
Deployment and Integration Specialist
The Norcross Group
www.NorcrossGroup.com

 >>  Hi Roberto,

 >>  I've CCed this reply to the linux-ha mailing list.

 >>  Roberto Zini wrote:

 >>  > Hi Alan !
 >>  > 
 >>  > In the past few days I tried you heartbeat solution on a couple of
 >>  > Linux boxes and so far I was impressed by the results I got !


 >>  Thanks!


 >>  > I'm trying to use the HB (heartbeat) solution as to allow a given
 >>  > process (eg, Apache running several CGI scripts) to operate on a
 >>  > SCSI disk which is shared between the above 2 boxes. Just to provide
 >>  > you with some numbers, I'm using a couple of Adaptec 29160 HA
 >>  (configured as 
 >>  > ID=14 on the first box and ID=13 on the second one) whose secondary bus
 >>  is 
 >>  > connected to an external SCSI disk configured as ID=5 (the primary SCSI
 >>  > bus is being used for the boot/root disk).
 >>  > 
 >>  > Let me preface that I'm neither a SCSI expert nor a Linux one but in
 >>  > my tests I've seen that both boxes are able to access the same 
 >>  > shared HD (which has been prepared with a Linux partition) at the same
 >>  > time (ie, they can "mount" it without problems) which can lead to data
 >>  > corruption if both OSes try to write the same chunk of data.
 >>  > 
 >>  > I'm wondering if there is an HW/SW solution which prevents the
 >>  "failover"
 >>  > box (from the HB point of view) from mounting the external disk when
 >>  it's 
 >>  > already being mounted by the primary box.


 >>  You could write a resource script which removes the /dev entry when the 
 >>  other side has the disk mounted.  Or you could do the equivalent at the 
 >>  kernel level like this:
 >>      echo "scsi-remove-single-device A 0 D 0" > /proc/scsi/scsi
 >>  to make the kernel believe the device is gone, and then also do
 >>      echo "scsi-add-single-device A 0 D 0" > /proc/scsi/scsi
 >>  to make it come back just before takeover.

 >>  Maybe someone should write such a resource script...

 >>  In this case A is number of the SCSI adapter according to /proc/scsi/scsi,
 >>  
 >>  and D is the logical drive number (I think this is the SCSI target ID).

 >>  Thanks to the IBM ServeRAID team for this cool tip.

 >>  But, you should still use a STONITH device to *GUARANTEE* that the other 
 >>  machine isn't using the disk.  A STONITH device is a smart power switch. 
 >>  Heartbeat supports around 8-10 types of STONITH devices.

 >>      -- Alan Robertson
 >>         alanr@unix.sh


 >>  --------------------------------------------------------------------------
 >>  ----
 >>  Linux HA Web Site:
 >>  http://linux-ha.org/
 >>  Linux HA HOWTO:
 >>  
 >>  http://metalab.unc.edu/pub/Linux/ALPHA/linux-ha/High-Availability-HOWTO.h
 >>  tml
 >>  --------------------------------------------------------------------------
 >>  ----