[gpfsug-discuss] maybe a silly question about "old school" gpfs

[Vic Cornell]

Hi Salvatore,

If you are doing the IO on the NSD server itself and it can see all of the NSDs it will use its "local” access to write to the LUNS.

You need some GPFS clients to see the workload spread across all of the NSD servers.

Vic



> On 5 Nov 2014, at 10:15, Salvatore Di Nardo <sdinardo at ebi.ac.uk> wrote:
> 
> Hello again,
> to understand better GPFS, recently i build up an test gpfs cluster using some old hardware that was going to be retired. THe storage was SAN devices, so instead to use native raids I went for the old school gpfs. the configuration is basically:
> 
> 3x servers 
> 3x san storages
> 2x san switches
> 
> I did no zoning, so all the servers can see all the LUNs, but on nsd creation I gave each LUN a primary, secondary and third server. with the following rule:
> 
> STORAGE
> primary
> secondary
> tertiary
> storage1
> server1
> server2	server3
> storage2	server2	server3	server1
> storage3	server3	server1	server2
> 
> looking at the mmcrnsd, it was my understanding that the primary server is the one that wrote on the NSD unless it fails, then the following server take the ownership of the lun.
> 
> Now come the question: 
> when i did from server 1 a dd surprisingly i discovered that server1 was writing to all the luns. the other 2 server was doing nothing. this behaviour surprises me because on GSS only the RG owner can write, so one server "ask" the other server to write to his own RG's.In fact on GSS can be seen a lot of ETH traffic and io/s on each server. While i understand that the situation it's different I'm puzzled about the fact that all the servers seems able to write to all the luns. 
> 
> SAN deviced usually should be connected to one server only, as paralled access could create data corruption. In environments where you connect a SAN to multiple servers ( example VMWARE cloud) its softeware task to avoid data overwriting between server ( and data corruption ).
> 
> Honestly, what  i was expecting is: server1 writing on his own luns, and data traffic ( ethernet) to the other 2 server , basically asking them to write on the other luns. I dont know if this behaviour its normal or not. I triied to find a documentation about that, but could not find any.
> 
> Could somebody  tell me if this "every server write to all the luns" its intended or not?
> 
> Thanks in advance,
> Salvatore
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