[gpfsug-discuss] Node expels

Simon Thompson S.J.Thompson at bham.ac.uk
Thu Jan 17 19:02:06 GMT 2019


So we've backed out a bunch of network tuning parameters we had set (based on the GPFS wiki pages), they've been set a while but um ... maybe they are causing issues.

Secondly, we've noticed in dump tscomm that we see connection broken to a node, and then the node ID is usually the same node, which is a bit weird to me.

We've also just updated firmware on the Intel nics (the x722) which is part of the Skylake board. And specifically its the newer skylake kit we see this problem on. We've a number of issues with the x722 firmware (like it won't even bring a link up when plugged into some of our 10GbE switches, but that's another story).

We've also dropped the bonded links from these nodes, just in case its related...

Simon

________________________________
From: gpfsug-discuss-bounces at spectrumscale.org [gpfsug-discuss-bounces at spectrumscale.org] on behalf of jlewars at us.ibm.com [jlewars at us.ibm.com]
Sent: 17 January 2019 14:30
To: Tomer Perry; gpfsug main discussion list
Cc: Yong Ze Chen
Subject: Re: [gpfsug-discuss] Node expels

>They always appear to be to a specific type of hardware with the same Ethernet controller,

That makes me think you might be seeing packet loss that could require ring buffer tuning (the defaults and limits will differ with different ethernet adapters).

The expel section in the slides on this page has been expanded to include a 'debugging expels section' (slides 19-20, which also reference ring buffer tuning):
https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/General%20Parallel%20File%20System%20(GPFS)/page/DEBUG%20Expels/comment/7e4f9433-7ca3-430f-b40b-94777c507381

Regards,
John Lewars
Spectrum Scale Performance, IBM Poughkeepsie




From:        Tomer Perry/Israel/IBM
To:        gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Cc:        John Lewars/Poughkeepsie/IBM at IBMUS, Yong Ze Chen/China/IBM at IBMCN
Date:        01/17/2019 08:28 AM
Subject:        Re: [gpfsug-discuss] Node expels
________________________________


Hi,

I was asked to elaborate a bit ( thus also adding John and Yong Ze Chen).

As written on the slide:
One of the best ways to determine if a network layer problem is root cause for an expel is to look at the low-level socket details dumped in the ‘extra’ log data (mmfs dump all) saved as part of automatic data collection on Linux GPFS nodes.

So, the idea is that in expel situation, we dump the socket state from the OS ( you can see the same using 'ss -i' for example).
In your example, it shows that the ca_state is 4, there are retransmits, high rto and all the point to a network problem.
You can find more details here: http://www.yonch.com/tech/linux-tcp-congestion-control-internals


Regards,

Tomer Perry
Scalable I/O Development (Spectrum Scale)
email: tomp at il.ibm.com
1 Azrieli Center, Tel Aviv 67021, Israel
Global Tel:    +1 720 3422758
Israel Tel:      +972 3 9188625
Mobile:         +972 52 2554625





From:        "Tomer Perry" <TOMP at il.ibm.com>
To:        gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date:        17/01/2019 13:46
Subject:        Re: [gpfsug-discuss] Node expels
Sent by:        gpfsug-discuss-bounces at spectrumscale.org
________________________________



Simon,

Take a look at http://files.gpfsug.org/presentations/2018/USA/Scale_Network_Flow-0.8.pdfslide 13.


Regards,

Tomer Perry
Scalable I/O Development (Spectrum Scale)
email: tomp at il.ibm.com
1 Azrieli Center, Tel Aviv 67021, Israel
Global Tel:    +1 720 3422758
Israel Tel:      +972 3 9188625
Mobile:         +972 52 2554625




From:        Simon Thompson <S.J.Thompson at bham.ac.uk>
To:        "gpfsug-discuss at spectrumscale.org" <gpfsug-discuss at spectrumscale.org>
Date:        17/01/2019 13:35
Subject:        [gpfsug-discuss] Node expels
Sent by:        gpfsug-discuss-bounces at spectrumscale.org
________________________________



We’ve recently been seeing quite a few node expels with messages of the form:

2019-01-17_11:19:30.882+0000: [W] The TCP connection to IP address 10.20.0.58 proto-pg-pf01.bear.cluster <c0n236> (socket 153) state is unexpected: state=1 ca_state=4 snd_cwnd=1 snd_ssthresh=5 unacked=5 probes=0 backoff=7 retransmits=7 rto=26496000 rcv_ssthresh=102828 rtt=6729 rttvar=12066 sacked=0 retrans=1 reordering=3 lost=5
2019-01-17_11:19:30.882+0000: [I] tscCheckTcpConn: Sending debug data collection request to node 10.20.0.58 proto-pg-pf01.bear.cluster
2019-01-17_11:19:30.882+0000: Sending request to collect TCP debug data to proto-pg-pf01.bear.cluster localNode
2019-01-17_11:19:30.882+0000: [I] Calling user exit script gpfsSendRequestToNodes: event sendRequestToNodes, Async command /usr/lpp/mmfs/bin/mmcommon.
2019-01-17_11:24:52.611+0000: [E] Timed out in 300 seconds waiting for a commMsgCheckMessages reply from node 10.20.0.58 proto-pg-pf01.bear.cluster. Sending expel message.

On the client node, we see messages of the form:

2019-01-17_11:19:31.101+0000: [N] sdrServ: Received Tcp data collection request from 10.10.0.33
2019-01-17_11:19:31.102+0000: [N] GPFS will attempt to collect Tcp debug data on this node.
2019-01-17_11:24:52.838+0000: [N] sdrServ: Received expel data collection request from 10.10.0.33
2019-01-17_11:24:52.838+0000: [N] GPFS will attempt to collect debug data on this node.
2019-01-17_11:25:02.741+0000: [N] This node will be expelled from cluster rds.gpfs.servers due to expel msg from 10.10.12.41 (b
ber-les-nsd01-data.bb2.cluster in rds.gpfs.server
2019-01-17_11:25:03.160+0000: [N] sdrServ: Received expel data collection request from 10.20.0.56

They always appear to be to a specific type of hardware with the same Ethernet controller, though the nodes are split across three data centres and we aren’t seeing link congestion on the links between them.

On the node I listed above, it’s not actually doing anything either as the software on it is still being installed (i.e. it’s not doing GPFS or any other IO other than a couple of home directories).

Any suggestions on what “(socket 153) state is unexpected” means?

Thanks

Simon

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