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<font size="-1">Hello again,<br>
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:<br>
<br>
3x servers <br>
3x san storages<br>
2x san switches<br>
<br>
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:<br>
<br>
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<table width="80%" border="1" cellpadding="2" cellspacing="2">
<tbody>
<tr>
<td valign="top"><font size="-1">STORAGE</font><br>
</td>
<td valign="top">primary<br>
</td>
<td valign="top">secondary<br>
</td>
<td valign="top">tertiary<br>
</td>
</tr>
<tr>
<td valign="top">storage1<br>
</td>
<td valign="top">server1<br>
</td>
<td valign="top">server2</td>
<td valign="top">server3</td>
</tr>
<tr>
<td valign="top">storage2</td>
<td valign="top">server2</td>
<td valign="top">server3</td>
<td valign="top">server1</td>
</tr>
<tr>
<td valign="top">storage3</td>
<td valign="top">server3</td>
<td valign="top">server1</td>
<td valign="top">server2</td>
</tr>
</tbody>
</table>
<font size="-1"><br>
<br>
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.<br>
<br>
Now come the question: <br>
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. <br>
<br>
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 ).<br>
<br>
Honestly, what i was expecting is: server1 writing on his own
luns, and data traffic ( ethernet) to the other 2 server ,
basically asking <b>them</b> 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.<br>
<br>
Could somebody tell me if this <u><i>"every server write to all
the luns"</i></u> its intended or not?<br>
<br>
Thanks in advance,<br>
Salvatore<br>
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