In case of SAN connectivity, all nodes can write to disks. This avoids going over the network to get to disks. Only when local access isn't present either due to connectivity or zoning will it use the defined NSD server.
If there is a need to have the node always use a NSD server, you can enforce it via mount option -o usensdserver=always If the first nsd server is down, it will use the next NSD server in the list. In general NSD servers are a priority list of servers rather than a primary/secondary config which is the case when using native raid. Also note that multiple nodes accessing the same disk will not cause corruption as higher level token mgmt in GPFS will take care of data consistency. Regards Kalyan C Gunda STSM, Elastic Storage Development Member of The IBM Academy of Technology EGL D Block, Bangalore From: Salvatore Di Nardo <[email protected]> To: gpfsug main discussion list <[email protected]> Date: 11/05/2014 03:44 PM Subject: [gpfsug-discuss] maybe a silly question about "old school" gpfs Sent by: [email protected] 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_______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at gpfsug.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss _______________________________________________ gpfsug-discuss mailing list gpfsug-discuss at gpfsug.org http://gpfsug.org/mailman/listinfo/gpfsug-discuss
