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<div class="moz-cite-prefix">Hi Salvatore,<br>
<br>
GSS and GPFS systems are different beasts.<br>
<br>
In a traditional GPFS configuration I would expect any NSD server
to write to any/all LUN's that it can see as a local disk
providing it's part of the same FS.<br>
<br>
In GSS there is effectively a software RAID level added on top of
the disks, with this I would expect only the RG owner to write
down to the vdisk.<br>
<br>
As for corruption, GPFS uses a token system to manage access to
LUN's, Metadata, etc.<br>
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<p>
Kind Regards,
</p>
<p>
<span class="signame">Laurence Horrocks-Barlow</span> <br>
<span class="sigtitle">Linux Systems Software Engineer</span>
<br>
<span class="sigcompany">OCF plc</span> <br>
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On 11/05/2014 10:33 AM, Salvatore Di Nardo wrote:<br>
</div>
<blockquote cite="mid:5459FD15.3070105@ebi.ac.uk" type="cite">
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I understand that my test its a bit particular because the client
was also one of the servers.<br>
Usually clients don't have direct access to the storages, but
still it made think, hot the things are supposed to work.<br>
<br>
For example i did another test with 3 dd's, one each server. All
the servers was writing to all the luns. <br>
In other words a lun was accessed in parallel by 3 servers. <br>
<br>
Its that a problem, or gpfs manage properly the concurrency and
avoid data corruption? <br>
I'm asking because i was not expecting a server to write to an NSD
he doesn't own, even if its locally available. <br>
I thought that the general availablity was for failover, not for
parallel access.<br>
<br>
<br>
Regards,<br>
Salvatore<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 05/11/14 10:22, Vic Cornell wrote:<br>
</div>
<blockquote
cite="mid:3F74C441-C25D-4F19-AD05-04AD897A08D3@gmail.com"
type="cite">
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charset=windows-1252">
Hi Salvatore,
<div class=""><br class="">
</div>
<div class="">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.</div>
<div class=""><br class="">
</div>
<div class="">You need some GPFS clients to see the workload
spread across all of the NSD servers.</div>
<div class=""><br class="">
</div>
<div class="">Vic</div>
<div class=""><br class="">
<div class=""><br class="">
</div>
<div class=""><br class="">
<div>
<blockquote type="cite" class="">
<div class="">On 5 Nov 2014, at 10:15, Salvatore Di
Nardo <<a moz-do-not-send="true"
href="mailto:sdinardo@ebi.ac.uk" class="">sdinardo@ebi.ac.uk</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<meta http-equiv="content-type" content="text/html;
charset=windows-1252" class="">
<div text="#000000" bgcolor="#FFFFFF" class=""> <font
class="" size="-1">Hello again,<br class="">
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
class="">
<br class="">
3x servers <br class="">
3x san storages<br class="">
2x san switches<br class="">
<br class="">
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 class="">
<br class="">
</font>
<table class="" border="1" cellpadding="2"
cellspacing="2" width="80%">
<tbody class="">
<tr class="">
<td class="" valign="top"><font class=""
size="-1">STORAGE</font><br class="">
</td>
<td class="" valign="top">primary<br class="">
</td>
<td class="" valign="top">secondary<br
class="">
</td>
<td class="" valign="top">tertiary<br class="">
</td>
</tr>
<tr class="">
<td class="" valign="top">storage1<br class="">
</td>
<td class="" valign="top">server1<br class="">
</td>
<td class="" valign="top">server2</td>
<td class="" valign="top">server3</td>
</tr>
<tr class="">
<td class="" valign="top">storage2</td>
<td class="" valign="top">server2</td>
<td class="" valign="top">server3</td>
<td class="" valign="top">server1</td>
</tr>
<tr class="">
<td class="" valign="top">storage3</td>
<td class="" valign="top">server3</td>
<td class="" valign="top">server1</td>
<td class="" valign="top">server2</td>
</tr>
</tbody>
</table>
<font class="" size="-1"><br class="">
<br class="">
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 class="">
<br class="">
Now come the question: <br class="">
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
class="">
<br class="">
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
class="">
<br class="">
Honestly, what i was expecting is: server1
writing on his own luns, and data traffic (
ethernet) to the other 2 server , basically asking
<b class="">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 class="">
<br class="">
Could somebody tell me if this <u class=""><i
class="">"every server write to all the luns"</i></u>
its intended or not?<br class="">
<br class="">
Thanks in advance,<br class="">
Salvatore<br class="">
</font> </div>
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class="">
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</blockquote>
</div>
<br class="">
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