[CentOS] scsi3 persistent reservations in cluster storage fencing

Tue May 24 16:10:14 UTC 2011
Devin Reade <gdr at gno.org>

--On Friday, May 20, 2011 02:28:18 PM -0700 John R Pierce
<pierce at hogranch.com> wrote:

> One question I have is: how well will this scale with several strings of 
> 100 SAS drives on the same HA pair of servers?
> Can SAS storage instead be fenced at the SES/expander level rather than 
> having to use reservations with each separate drive?

It's been a few years since I've used SCSI reservations as a fencing
method (as in about the time that wide SCSI was taking over from narrow
SCSI, and while it fenced nicely, it sometimes caused bus errors when
you detached the dead node from the bus).

However if you are using a set of disks as a logical unit from
the cluster's perspective (like having set of disks acting as a RAID
device), then IIRC it is sufficient to use a reservation on a single
disk as your fence for the entire disk set (rather than using a 
reservation on every single disk).  Of course, of your storage cabinet
has a few different disk sets in it, you'd need additional reservations
(one per set).

But, as I said, it's been a few years so I'd investigate it more rather
than depending on *just* the above comment.  In recent years I've tended
to use various mechanisms to kill power to the node as my preferred 
fencing method.

The linux-ha and pacemaker lists may be a better source of current