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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