[gpfsug-discuss] GPFS - pagepool data protection?

[Pavel Pokorny]

Hi,
thanks. A I understand the write process to GPFS filesystem:

1. Application on a node makes write call
2. Token Manager stuff is done to coordinate the required-byte-range
3. mmfsd gets metadata from the file’s metanode
4. mmfsd acquires a buffer from the page pool
5. Data is moved from application data buffer to page pool buffer
6. VSD layer copies data from the page pool to the send pool
 and so on.

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?
Will GPFS use journal to get to stable state?
Thank you, Pavel

--
Ing. Pavel Pokorný
DATERA s.r.o. | Ovocný trh 580/2 | Praha | Czech Republic
www.datera.cz | Mobil: +420 602 357 194 | E-mail: pavel.pokorny at datera.cz


On Sat, Nov 8, 2014 at 1:00 PM, <gpfsug-discuss-request at gpfsug.org> wrote:

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>    1. Re: GPFS - pagepool data protection? (Dean Hildebrand)
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> Message: 1
> Date: Fri, 7 Nov 2014 23:42:06 +0100
> From: Dean Hildebrand <dhildeb at us.ibm.com>
> To: gpfsug main discussion list <gpfsug-discuss at gpfsug.org>
> Subject: Re: [gpfsug-discuss] GPFS - pagepool data protection?
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>
> Hi Paul,
>
> GPFS correctly implements POSIX semantics and NFS close-to-open semantics.
> Its a little complicated, but effectively what this means is that when the
> application issues certain calls to ensure data/metadata is "stable" (e.g.,
> fsync), then it is guaranteed to be stable.  It also controls ordering
> between nodes among many other things.  As part of making sure data is
> stable, the GPFS recovery journal is used in a variety of instances.
>
> With VMWare ESX using NFS to GPFS, then the same thing occurs, except the
> situation is even more simple since every write request will have the
> 'stable' flag set, ensuring it does writethrough to the storage system.
>
> Dean Hildebrand
> IBM Almaden Research Center
>
>
>
>
> From:   Pavel Pokorny <pavel.pokorny at datera.cz>
> To:     gpfsug-discuss at gpfsug.org
> Date:   11/07/2014 03:15 AM
> Subject:        [gpfsug-discuss] GPFS - pagepool data protection?
> Sent by:        gpfsug-discuss-bounces at gpfsug.org
>
>
>
> Hello to all,
> I would like to ask question about pagepool and protection of data written
> through pagepool.
> Is there a possibility of loosing data written to GPFS in situation that
> data are stored in pagepool but still not written to disks?
> I think that for regular file system work this can be solved using GPFS
> journal. What about using GPFS as a NFS store for VMware datastores?
> Thank you for your answers,
> Pavel
> --
> Ing. Pavel Pokorn?
> DATERA s.r.o.?|?Ovocn? trh 580/2?|?Praha?|?Czech Republic
> www.datera.cz?|?Mobil:?+420 602 357 194?|?E-mail:?pavel.pokorny at datera.cz
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