Re: [gpfsug-discuss] snapshots causing filesystem quiesce

[Jordi Caubet Serrabou]

Ivano,

 

if it happens frequently, I would recommend to open a support case.

 

The creation or deletion of a snapshot requires a quiesce of the nodes to obtain a consistent point-in-time image of the file system and/or update some internal structures afaik. Quiesce is required for nodes at the storage cluster but also remote clusters. Quiesce means stop activities (incl. I/O) for a short period of time to get such consistent image. Also waiting to flush any data in-flight to disk that does not allow a consistent point-in-time image.

 

Nodes receive a quiesce request and acknowledge when ready. When all nodes acknowledge, snapshot operation can proceed and immediately I/O can resume. It usually takes few seconds at most and the operation performed is short but time I/O is stopped depends of how long it takes to quiesce the nodes. If some node take longer to agree stop the activities, such node will be delay the completion of the quiesce and keep I/O paused on the rest.

There could many things while some nodes delay quiesce ack.

 

The larger the cluster, the more difficult it gets. The more network congestion or I/O load, the more difficult it gets. I recommend to open a ticket for support to try to identify the root cause of which nodes not acknowledge the quiesce  and maybe find the root cause. If I recall some previous thread, default timeout was 60 seconds which match your log message. After such timeout, snapshot is considered failed to complete.

 

Support might help you understand the root cause and provide some recommendations if it happens frequently.

 

Best Regards,
--
Jordi Caubet Serrabou
IBM Storage Client Technical Specialist (IBM Spain)

 

----- Original message -----
From: "Talamo Ivano Giuseppe (PSI)" <ivano.tal...@psi.ch>
Sent by: gpfsug-discuss-boun...@spectrumscale.org
To: "gpfsug main discussion list" <gpfsug-discuss@spectrumscale.org>
Cc:
Subject: [EXTERNAL] Re: [gpfsug-discuss] snapshots causing filesystem quiesce
Date: Wed, Feb 2, 2022 11:45 AM
 

Hello Andrew,

 

Thanks for your questions.

 

We're not experiencing any other issue/slowness during normal activity.

The storage is a Lenovo DSS appliance with a dedicated SSD enclosure/pool for metadata only.

 

The two NSD servers have 750GB of RAM and 618 are configured as pagepool.

 

The issue we see is happening on both the two filesystems we have:

 

- perf filesystem:

 - 1.8 PB size (71% in use)

 - 570 milions of inodes (24% in use)

 

- tiered filesystem:

 - 400 TB size (34% in use)

 - 230 Milions of files (60% in use)

 

Cheers,

Ivano

 

 

 

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Ivano Talamo

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Telefon: +41 56 310 47 11

E-Mail: ivano.tal...@psi.ch

 

 

 

---

From: gpfsug-discuss-boun...@spectrumscale.org <gpfsug-discuss-boun...@spectrumscale.org> on behalf of Andrew Beattie <abeat...@au1.ibm.com>
Sent: Wednesday, February 2, 2022 10:33 AM
To: gpfsug main discussion list
Subject: Re: [gpfsug-discuss] snapshots causing filesystem quiesce

 

Ivano,

 

How big is the filesystem in terms of number of files?

How big is the filesystem in terms of capacity? 

Is the Metadata on Flash or Spinning disk? 

Do you see issues when users do an LS of the filesystem or only when you are doing snapshots.

 

How much memory do the NSD servers have?

How much is allocated to the OS / Spectrum

 Scale  Pagepool
 

Regards

 

Andrew Beattie

Technical Specialist - Storage for Big Data & AI

IBM Technology Group

IBM Australia & New Zealand

P. +61 421 337 927

E. abeat...@au1.ibm.com

 

 

 

On 2 Feb 2022, at 19:14, Talamo Ivano Giuseppe (PSI) <ivano.tal...@psi.ch> wrote:
 



 

Dear all,

 

Since a while we are experiencing an issue when dealing with snapshots.

Basically what happens is that when deleting a fileset snapshot (and maybe also when creating new ones) the filesystem becomes inaccessible on the clients for the duration of the operation (can take a few minutes).

 

The clients and the storage are on two different clusters, using remote cluster mount for the access.

 

On the log files many lines like the following appear (on both clusters):

Snapshot whole quiesce of SG perf from xbldssio1 on this node lasted 60166 msec

 

By looking around I see we're not the first one. I am wondering if that's considered an unavoidable part of the snapshotting and if there's any tunable that can improve the situation. Since when this occurs all the clients are stuck and users are very quick to complain.

 

If it can help, the clients are running GPFS 5.1.2-1 while the storage cluster is on 5.1.1-0.

 

Thanks,

Ivano

 

 

 

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