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

Jonathan Buzzard jonathan at buzzard.me.uk
Wed Nov 5 10:38:48 GMT 2014


On Wed, 2014-11-05 at 10:15 +0000, Salvatore Di Nardo wrote:

[SNIP]

> 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. 

The difference is that in GSS the NSD servers are in effect doing
software RAID on the disks. Therefore they and they alone can write to
the NSD. In the traditional setup the NSD is on a RAID device on SAN
controller and multiple machines are able to access the block device at
the same time with token management in GPFS preventing corruption.

I guess from a technical perspective you could have the GSS software
RAID distributed between the NSD servers, but that would be rather more
complex software and it is no surprise IBM have gone down the easy
route.

JAB.

-- 
Jonathan A. Buzzard                 Email: jonathan (at) buzzard.me.uk
Fife, United Kingdom.





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