[Linux-cluster] Using GFS without a network?
Keith Hopkins
hne at hopnet.net
Wed Sep 7 09:43:13 UTC 2005
Steve Wilcox wrote:
> On Tue, 2005-09-06 at 20:06 -0400, Steve Wilcox wrote:
>
>>On Wed, 2005-09-07 at 00:57 +0200, Andreas Brosche wrote:
>>
>>
>>>>- Multi-initator SCSI buses do not work with GFS in any meaningful way,
>>>>regardless of what the host controller is.
>>>>Ex: Two machines with different SCSI IDs on their initiator connected to
>>>>the same physical SCSI bus.
>>>
>>>Hmm... don't laugh at me, but in fact that's what we're about to set up.
>>>
>>>I've read in Red Hat's docs that it is "not supported" because of
>>>performance issues. Multi-initiator buses should comply to SCSI
>>>standards, and any SCSI-compliant disk should be able to communicate
>>>with the correct controller, if I've interpreted the specs correctly. Of
>>>course, you get arbitrary results when using non-compliant hardware...
>>>What are other issues with multi-initiator buses, other than performance
>>>loss?
>>
>>I set up a small 2 node cluster this way a while back, just as a testbed
>>for myself. Much as I suspected, it was severely unstable because of
>>the storage configuration, even occasionally causing both nodes to crash
>>when one was rebooted due to SCSI bus resets. I tore it down and
>>rebuilt it several times, configuring it as a simple failover cluster
>>with RHEL3 and RHEL4, a GFS cluster under RHEL4 and Fedora4, and as an
>>openSSI cluster using Fedora3. All tested configurations were equally
>>crash-happy due to the bus resets.
>>
>>My configuration consisted of a couple of old Compaq deskpro PC's, each
>>with a single ended Symbiosis card (set to different SCSI ID's
>>obviously) and an external DEC BA360 jbod shelf with 6 drives. The bus
>>resets might be mitigated somewhat by using HVD SCSI and Y-cables with
>>external terminators, but from my previous experience with other
>>clusters that used this technique (DEC ASE and HP-ux service guard), bus
>>resets will always be a thorn in your side without a separate,
>>independent raid controller to act as a go-between. Calling these
>>configurations simply "not supported" is an understatement - this type
>>of config is guaranteed trouble. I'd never set up a cluster this way
>>unless I'm the only one using it, and only then if I don't care one
>>little bit about crashes and data corruption. My two cents.
>>
>>-steve
>
>
>
> Small clarification - Although clusters from DEC, HP, and even
> DigiComWho?Paq's TruCluster can be made to work (sort of) on multi-
> initiator SCSI busses, IIRC it was never a supported option for any of
> them (much like RedHat's offering). I doubt any sane company would ever
> support that type of config.
>
> -steve
>
HP-UX ServiceGuard words well with multi-initiator SCSI configurations, and is fully supported by HP. It is sold that way for small 2-4 node clusters when cost is an issue, although FC has become a big favorite (um...money maker) in recent years. Yes, SCSI bus resets are a pain, but they are handled by HP-UX, not ServiceGuard.
--Keith
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