[gpfsug-discuss] Multi-cluster question (was Re: gpfsug-discuss Digest, Vol 100, Issue 32)

[Avila, Geoffrey]

The local-block-device method of I/O is what is usually termed "SAN mode";
right?

On Sun, May 31, 2020 at 12:47 PM Jan-Frode Myklebust <janfrode at tanso.net>
wrote:

>
> No, this is a common misconception.  You don’t need any NSD servers. NSD
> servers are only needed if you have nodes without direct block access.
>
> Remote cluster or not, disk access will be over local block device
> (without involving NSD servers in any way), or NSD server if local access
> isn’t available. NSD-servers are not «arbitrators» over access to a disk,
> they’re just stupid proxies of IO commands.
>
>
>   -jf
>
> søn. 31. mai 2020 kl. 11:31 skrev Jonathan Buzzard <
> jonathan.buzzard at strath.ac.uk>:
>
>> On 29/05/2020 20:55, Stephen Ulmer wrote:
>> > I have a question about multi-cluster, but it is related to this thread
>> > (it would be solving the same problem).
>> >
>> > Let’s say we have two clusters A and B, both clusters are normally
>> > shared-everything with no NSD servers defined.
>>
>> Er, even in a shared-everything all nodes fibre channel attached you
>> still have to define NSD servers. That is a given NSD has a server (or
>> ideally a list of servers) that arbitrate the disk. Unless it has
>> changed since 3.x days. Never run a 4.x or later with all the disks SAN
>> attached on all the nodes.
>>
>> > We want cluster B to be
>> > able to use a file system in cluster A.  If I zone the SAN such that
>> > cluster B can see all of cluster A’s disks, can I then define a
>> > multi-cluster relationship between them and mount a file system from A
>> on B?
>> >
>> > To state it another way, must B's I/O for the foreign file system pass
>> > though NSD servers in A, or can B’s nodes discover that they have
>> > FibreChannel paths to those disks and use them?
>> >
>>
>> My understanding is that remote cluster mounts have to pass through the
>> NSD servers.
>>
>>
>> JAB.
>>
>> --
>> Jonathan A. Buzzard                         Tel: +44141-5483420
>> HPC System Administrator, ARCHIE-WeSt.
>> University of Strathclyde, John Anderson Building, Glasgow. G4 0NG
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