[CentOS] scsi3 persistent reservations in cluster storage fencing

Sat May 21 23:44:14 UTC 2011
Steven Crothers <steven.crothers at gmail.com>

You might be able to go a simpler route, try building a GFBD between
them and sharing the storage that way. I personally have never tried
it, but that might give you the HA you're looking for while staying
withing the CentOS/Upstream packaging. One added benefit is the
ability to scale vertically and horizontally with a setup like that
with failover and quorum. Heck, toss in a little heartbeat scripting
and you could call it an auto-healing storage cloud.

Good luck!

On Fri, May 20, 2011 at 5:28 PM, John R Pierce <pierce at hogranch.com> wrote:
> I'm interested in the idea of sharing a bunch of SAS JBOD devices
> between two CentOS servers in an active-standby HA cluster sort of
> arrangement, and found something about using scsi3 persistent
> reservations as a fencing method.    I'm not finding a lot of specifics
> about how this works, or how you configure two initiator systems on a
> SAS chain.   I don't have any suitable hardware for running any tests or
> evaluations yet.
> general idea:  2 centos servers each with 8 port external SAS cards (2
> x4), cascaded through a SAS box-o-disks with a whole bunch of SAS dual
> ported drives, to implement high availability large nearline
> storage.       all storage configured as JBOD, using linux md raid or
> lvm mirroring. drives should only be accessible by the currently active
> server, with heartbeat managing the fencing.
> here's a hardware block diagram
> http://freescruz.com/shared-sas.jpg
> This is about the only details I've found on scsi persistant
> reservations and linux HA
> http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Configuration_Example_-_Fence_Devices/SCSI_Configuration.html
> 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?
> --
> john r pierce                            N 37, W 123
> santa cruz ca                         mid-left coast
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Steven Crothers
steven.crothers at gmail.com