[CentOS] Re: ATA-over-Ethernet v's iSCSI -- CORAID is NOT SAN, also check multi-target SAS

Tarun Reddy treddy at rallydev.com
Wed Nov 9 00:25:17 UTC 2005

On Nov 8, 2005, at 5:19 AM, Bryan J. Smith wrote:

> On Tue, 2005-11-08 at 15:16 +1100, Nick Bryant wrote:
>> When I said shared storage I didn't mean it had to be accessed at  
>> the same
>> time from all hosts. The RHEL cluster suite in an active/standby  
>> setup
>> actually mounts the partitions as a host changes from standby to
>> active after its sure the active host hasn't got access anymore  
>> with a
>> "lights out" OoB setup.
>> Well that was my understanding of how it worked anyhow?
> Yes, but you're missing a key point.  The system designated for  
> failover
> is still mounting the volume -- even if by standby.  Think of it as a
> "read-only" mount that tracks changes done by the other system with  
> the
> "read/write" (I know this is a mega-oversimplification).  And when it
> does fail-over, it still has to be allowed to mount it when the other
> system may be in a state that the target device believes is still
> accessing it.

Just one additional point. RH cluster suite requires (at least it did  
in RHEL3 clustering) two shared raw partitions to store state  
information and (I believe) some heartbeating.

This blows AoE out for anything with the cluster suite.

RedHat Clustering (again in 3), does not mount both volumes  
simultaneously for normal services however. When a node fails over,  
it is forcibly umounted on one system and remounted on the other.  
This means you can use ext3 with cluster suite. But the point above  
leads you to need a block level device.


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