Re: Issues with Ceph network redundancy using L2 MC-LAG
Do you observe the same behaviour when you pull a cable? Maybe a flapping port might cause this kind of behaviour, other than that you should't see any network disconnects. Are you sure about LACP configuration, what is the output of 'cat /proc/net/bonding/bond0' On Tue, Jun 15, 2021 at 7:19 PM huxiaoyu@horebdata.cn <huxiaoyu@horebdata.cn> wrote:
Dear Cephers,
I encountered the following networking issue several times, and i wonder whether there is a solution for networking HA solution.
We build ceph using L2 multi chassis link aggregation group (MC-LAG ) to provide switch redundancy. On each host, we use 802.3ad, LACP mode for NIC redundancy. However, we observe several times, when a single network port, either the cable, or the SFP+ optical module fails, Ceph cluster is badly affected by networking, although in theory it should be able to tolerate.
Did i miss something important here? and how to really achieve networking HA in Ceph cluster?
best regards,
Samuel
huxiaoyu@horebdata.cn _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
When i pull out the cable, then the bond is working properly. Does it mean that the port is somehow flapping? Ping can still work, but the iperf test yields very low results. huxiaoyu@horebdata.cn From: Serkan Çoban Date: 2021-06-15 18:47 To: huxiaoyu@horebdata.cn CC: ceph-users Subject: Re: [ceph-users] Issues with Ceph network redundancy using L2 MC-LAG Do you observe the same behaviour when you pull a cable? Maybe a flapping port might cause this kind of behaviour, other than that you should't see any network disconnects. Are you sure about LACP configuration, what is the output of 'cat /proc/net/bonding/bond0' On Tue, Jun 15, 2021 at 7:19 PM huxiaoyu@horebdata.cn <huxiaoyu@horebdata.cn> wrote:
Dear Cephers,
I encountered the following networking issue several times, and i wonder whether there is a solution for networking HA solution.
We build ceph using L2 multi chassis link aggregation group (MC-LAG ) to provide switch redundancy. On each host, we use 802.3ad, LACP mode for NIC redundancy. However, we observe several times, when a single network port, either the cable, or the SFP+ optical module fails, Ceph cluster is badly affected by networking, although in theory it should be able to tolerate.
Did i miss something important here? and how to really achieve networking HA in Ceph cluster?
best regards,
Samuel
huxiaoyu@horebdata.cn _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
With an unstable link/port you could see the issues you describe. Ping doesn’t have the packet rate for you to necessarily have a packet in transit at exactly the same time as the port fails temporarily. Iperf on the other hand could certainly show the issue, higher packet rate and more likely to have packets in flight at the time of a link fail...combined with packet loss/retries gives poor throughput. Depending on what you want to happen, there are a number of tuning options both on the switches and Linux. If you want the LAG to be down if any link fails, the you should be able to config this on the switches and/or Linux (minimum number of links = 2 if you have 2 links in the lag). You can also tune the link monitoring, how frequently the links are checked (e.g. miimon) etc. Bringing this value down from the default of 100ms may allow you to detect a link failure more quickly. But you then run into the chance if detecting a transient failure that wouldn’t have caused any issues....and the LAG becoming more unstable. Flapping/unstable links are the worst kind of situation. Ideally you’d pick that up quickly from monitoring/alerts and either fix immediately or take the link down until you can fix it. I run 2x10G from my hosts into separate switches (Dell S series – VLT between switches). Pulling a single interface has no impact on Ceph, any packet loss is tiny and we’re not exceeding 10G bandwidth per host. If you’re running 1G links and the LAG is already busy, a link failure could be causing slow writes to the host, just down to congestion...which then starts to impact the wider cluster based on how Ceph works. Just caveating the above with - I’m relatively new to Ceph myself.... Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows 10 From: huxiaoyu@horebdata.cn<mailto:huxiaoyu@horebdata.cn> Sent: 15 June 2021 17:52 To: Serkan Çoban<mailto:cobanserkan@gmail.com> Cc: ceph-users<mailto:ceph-users@ceph.io> Subject: [ceph-users] Re: Issues with Ceph network redundancy using L2 MC-LAG When i pull out the cable, then the bond is working properly. Does it mean that the port is somehow flapping? Ping can still work, but the iperf test yields very low results. huxiaoyu@horebdata.cn From: Serkan Çoban Date: 2021-06-15 18:47 To: huxiaoyu@horebdata.cn CC: ceph-users Subject: Re: [ceph-users] Issues with Ceph network redundancy using L2 MC-LAG Do you observe the same behaviour when you pull a cable? Maybe a flapping port might cause this kind of behaviour, other than that you should't see any network disconnects. Are you sure about LACP configuration, what is the output of 'cat /proc/net/bonding/bond0' On Tue, Jun 15, 2021 at 7:19 PM huxiaoyu@horebdata.cn <huxiaoyu@horebdata.cn> wrote:
Dear Cephers,
I encountered the following networking issue several times, and i wonder whether there is a solution for networking HA solution.
We build ceph using L2 multi chassis link aggregation group (MC-LAG ) to provide switch redundancy. On each host, we use 802.3ad, LACP mode for NIC redundancy. However, we observe several times, when a single network port, either the cable, or the SFP+ optical module fails, Ceph cluster is badly affected by networking, although in theory it should be able to tolerate.
Did i miss something important here? and how to really achieve networking HA in Ceph cluster?
best regards,
Samuel
huxiaoyu@horebdata.cn _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
_______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
On Jun 15, 2021, at 10:26 AM, Andrew Walker-Brown <andrew_jbrown@hotmail.com> wrote:
With an unstable link/port you could see the issues you describe. Ping doesn’t have the packet rate for you to necessarily have a packet in transit at exactly the same time as the port fails temporarily. Iperf on the other hand could certainly show the issue, higher packet rate and more likely to have packets in flight at the time of a link fail...combined with packet loss/retries gives poor throughput.
Depending on what you want to happen, there are a number of tuning options both on the switches and Linux. If you want the LAG to be down if any link fails, the you should be able to config this on the switches and/or Linux (minimum number of links = 2 if you have 2 links in the lag).
Or ensure that the links are active/active. Some of the trickiest situations I’ve encountered are when a bond is configured for active/backup, and there’s a latent issue with the backup link. Active goes down, and the bond is horqued. Another is when the backup link has CRC errors that only show up on the switch side, or when a configuration error causes packets sent over one of the links to be blackholed.
Flapping/unstable links are the worst kind of situation. Ideally you’d pick that up quickly from monitoring/alerts and either fix immediately or take the link down until you can fix it.
This. Flakiness on a cluster/replciation network is one reason to favor not having one, it removes certain flappy situations and OSDs are more likely up for real, or down hard.
I run 2x 10G on my hosts, and i would tolerate one bond with one link down. From what you suggest, i will check link monitoring, to make sure the failing link will be removed automatically, without the requirement for manually pulling out the cable. thanks and best regards, samuel huxiaoyu@horebdata.cn From: Andrew Walker-Brown Date: 2021-06-15 19:26 To: huxiaoyu@horebdata.cn; Serkan Çoban CC: ceph-users Subject: RE: [ceph-users] Re: Issues with Ceph network redundancy using L2 MC-LAG With an unstable link/port you could see the issues you describe. Ping doesn’t have the packet rate for you to necessarily have a packet in transit at exactly the same time as the port fails temporarily. Iperf on the other hand could certainly show the issue, higher packet rate and more likely to have packets in flight at the time of a link fail...combined with packet loss/retries gives poor throughput. Depending on what you want to happen, there are a number of tuning options both on the switches and Linux. If you want the LAG to be down if any link fails, the you should be able to config this on the switches and/or Linux (minimum number of links = 2 if you have 2 links in the lag). You can also tune the link monitoring, how frequently the links are checked (e.g. miimon) etc. Bringing this value down from the default of 100ms may allow you to detect a link failure more quickly. But you then run into the chance if detecting a transient failure that wouldn’t have caused any issues....and the LAG becoming more unstable. Flapping/unstable links are the worst kind of situation. Ideally you’d pick that up quickly from monitoring/alerts and either fix immediately or take the link down until you can fix it. I run 2x10G from my hosts into separate switches (Dell S series – VLT between switches). Pulling a single interface has no impact on Ceph, any packet loss is tiny and we’re not exceeding 10G bandwidth per host. If you’re running 1G links and the LAG is already busy, a link failure could be causing slow writes to the host, just down to congestion...which then starts to impact the wider cluster based on how Ceph works. Just caveating the above with - I’m relatively new to Ceph myself.... Sent from Mail for Windows 10 From: huxiaoyu@horebdata.cn Sent: 15 June 2021 17:52 To: Serkan Çoban Cc: ceph-users Subject: [ceph-users] Re: Issues with Ceph network redundancy using L2 MC-LAG When i pull out the cable, then the bond is working properly. Does it mean that the port is somehow flapping? Ping can still work, but the iperf test yields very low results. huxiaoyu@horebdata.cn From: Serkan Çoban Date: 2021-06-15 18:47 To: huxiaoyu@horebdata.cn CC: ceph-users Subject: Re: [ceph-users] Issues with Ceph network redundancy using L2 MC-LAG Do you observe the same behaviour when you pull a cable? Maybe a flapping port might cause this kind of behaviour, other than that you should't see any network disconnects. Are you sure about LACP configuration, what is the output of 'cat /proc/net/bonding/bond0' On Tue, Jun 15, 2021 at 7:19 PM huxiaoyu@horebdata.cn <huxiaoyu@horebdata.cn> wrote:
Dear Cephers,
I encountered the following networking issue several times, and i wonder whether there is a solution for networking HA solution.
We build ceph using L2 multi chassis link aggregation group (MC-LAG ) to provide switch redundancy. On each host, we use 802.3ad, LACP mode for NIC redundancy. However, we observe several times, when a single network port, either the cable, or the SFP+ optical module fails, Ceph cluster is badly affected by networking, although in theory it should be able to tolerate.
Did i miss something important here? and how to really achieve networking HA in Ceph cluster?
best regards,
Samuel
huxiaoyu@horebdata.cn _______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
_______________________________________________ ceph-users mailing list -- ceph-users@ceph.io To unsubscribe send an email to ceph-users-leave@ceph.io
participants (4)
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Andrew Walker-Brown
-
Anthony D'Atri
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huxiaoyu＠horebdata.cn
-
Serkan Çoban