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<p><font size="2" face="sans-serif">Hi Pavel,</font><br>
<br>
<font size="2" face="sans-serif">You are more or less right in your description, but the key that I tried to convey in my first email is that GPFS only obey's POSIX. So your question can be answered by looking at how your application performs the write and does your application ask to make the data live only in the pagepool or on stable storage. By default posix says that file create and writes are unstable, so just doing a write puts it in the pagepool and will be lost if a crash occurs immediately after. To make it stable, the application must do something in posix to make it stable, of which there are many ways to do so, including but not limited to O_SYNC, DIO, some form of fsync post write, etc, etc...</font><br>
<font size="2" face="sans-serif"><br>
Dean Hildebrand<br>
IBM Almaden Research Center<br>
</font><br>
<br>
<img width="16" height="16" src="cid:1__=07BBF702DFE39A688f9e8a93df938@us.ibm.com" border="0" alt="Inactive hide details for Pavel Pokorny ---11/12/2014 04:21:11 AM---Hi, thanks. A I understand the write process to GPFS filesy"><font size="2" color="#424282" face="sans-serif">Pavel Pokorny ---11/12/2014 04:21:11 AM---Hi, thanks. A I understand the write process to GPFS filesystem:</font><br>
<br>
<font size="1" color="#5F5F5F" face="sans-serif">From: </font><font size="1" face="sans-serif">Pavel Pokorny <pavel.pokorny@datera.cz></font><br>
<font size="1" color="#5F5F5F" face="sans-serif">To: </font><font size="1" face="sans-serif">gpfsug-discuss@gpfsug.org</font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Date: </font><font size="1" face="sans-serif">11/12/2014 04:21 AM</font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Subject: </font><font size="1" face="sans-serif">Re: [gpfsug-discuss] GPFS - pagepool data protection?</font><br>
<font size="1" color="#5F5F5F" face="sans-serif">Sent by: </font><font size="1" face="sans-serif">gpfsug-discuss-bounces@gpfsug.org</font><br>
<hr width="100%" size="2" align="left" noshade style="color:#8091A5; "><br>
<br>
<br>
<font size="3" face="serif">Hi,</font><br>
<font size="3" face="serif">thanks. A I understand the write process to GPFS filesystem:</font><br>
<br>
<font size="3" face="serif">1. Application on a node makes write call</font><br>
<font size="3" face="serif">2. Token Manager stuff is done to coordinate the required-byte-range</font><br>
<font size="3" face="serif">3. mmfsd gets metadata from the file’s metanode</font><br>
<font size="3" face="serif">4. mmfsd acquires a buffer from the page pool</font><br>
<font size="3" face="serif">5. Data is moved from application data buffer to page pool buffer</font><br>
<font size="3" face="serif">6. VSD layer copies data from the page pool to the send pool</font><br>
<font size="3" face="serif"> and so on.</font><br>
<br>
<font size="3" face="serif">What I am looking at and want to clarify is step 5. Situation when data is moved to page pool. What happen if the server will crash at tjis point?</font><br>
<font size="3" face="serif">Will GPFS use journal to get to stable state?</font><br>
<font size="3" face="serif">Thank you, Pavel</font><br>
<br>
<font size="2" color="#333333" face="Arial"><b>--</b></font><br>
<font size="2" color="#333333" face="Arial"><b>Ing. Pavel Pokorný</b></font><br>
<font size="2" color="#333333" face="Arial">DATERA s.r.o. </font><font size="2" color="#FF0000" face="Arial">|</font><font size="2" color="#333333" face="Arial"> Ovocný trh 580/2 </font><font size="2" color="#FF0000" face="Arial">|</font><font size="2" color="#333333" face="Arial"> Praha </font><font size="2" color="#FF0000" face="Arial">|</font><font size="2" color="#333333" face="Arial"> Czech Republic</font><br>
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<br>
<font size="3" face="serif">On Sat, Nov 8, 2014 at 1:00 PM, <</font><a href="mailto:gpfsug-discuss-request@gpfsug.org" target="_blank"><font size="3" color="#0000FF" face="serif"><u>gpfsug-discuss-request@gpfsug.org</u></font></a><font size="3" face="serif">> wrote:</font>
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1. Re: GPFS - pagepool data protection? (Dean Hildebrand)<br>
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Date: Fri, 7 Nov 2014 23:42:06 +0100<br>
From: Dean Hildebrand <</font><a href="mailto:dhildeb@us.ibm.com"><font size="3" color="#0000FF" face="serif"><u>dhildeb@us.ibm.com</u></font></a><font size="3" face="serif">><br>
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Subject: Re: [gpfsug-discuss] GPFS - pagepool data protection?<br>
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Hi Paul,<br>
<br>
GPFS correctly implements POSIX semantics and NFS close-to-open semantics.<br>
Its a little complicated, but effectively what this means is that when the<br>
application issues certain calls to ensure data/metadata is "stable" (e.g.,<br>
fsync), then it is guaranteed to be stable. It also controls ordering<br>
between nodes among many other things. As part of making sure data is<br>
stable, the GPFS recovery journal is used in a variety of instances.<br>
<br>
With VMWare ESX using NFS to GPFS, then the same thing occurs, except the<br>
situation is even more simple since every write request will have the<br>
'stable' flag set, ensuring it does writethrough to the storage system.<br>
<br>
Dean Hildebrand<br>
IBM Almaden Research Center<br>
<br>
<br>
<br>
<br>
From: Pavel Pokorny <</font><a href="mailto:pavel.pokorny@datera.cz"><font size="3" color="#0000FF" face="serif"><u>pavel.pokorny@datera.cz</u></font></a><font size="3" face="serif">><br>
To: </font><a href="mailto:gpfsug-discuss@gpfsug.org"><font size="3" color="#0000FF" face="serif"><u>gpfsug-discuss@gpfsug.org</u></font></a><font size="3" face="serif"><br>
Date: 11/07/2014 03:15 AM<br>
Subject: [gpfsug-discuss] GPFS - pagepool data protection?<br>
Sent by: </font><a href="mailto:gpfsug-discuss-bounces@gpfsug.org"><font size="3" color="#0000FF" face="serif"><u>gpfsug-discuss-bounces@gpfsug.org</u></font></a><font size="3" face="serif"><br>
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<br>
<br>
Hello to all,<br>
I would like to ask question about pagepool and protection of data written<br>
through pagepool.<br>
Is there a possibility of loosing data written to GPFS in situation that<br>
data are stored in pagepool but still not written to disks?<br>
I think that for regular file system work this can be solved using GPFS<br>
journal. What about using GPFS as a NFS store for VMware datastores?<br>
Thank you for your answers,<br>
Pavel<br>
--<br>
Ing. Pavel Pokorn?<br>
DATERA s.r.o.?|?Ovocn? trh 580/2?|?Praha?|?Czech Republic</font><font size="3" color="#0000FF" face="serif"><u><br>
</u></font><a href="http://www.datera.cz?%7C?Mobil:?+420" target="_blank"><font size="3" color="#0000FF" face="serif"><u>www.datera.cz?|?Mobil:?+420</u></font></a><font size="3" face="serif"> 602 357 194?|?E-mail:?</font><a href="mailto:pavel.pokorny@datera.cz"><font size="3" color="#0000FF" face="serif"><u>pavel.pokorny@datera.cz</u></font></a><font size="3" face="serif"><br>
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