[gpfsug-discuss] Steps for gracefully handling bandwidth reduction during network maintenance

[Christopher Black]

The man page indicates that maxMBpS can be used to "artificially limit how much I/O one node can put on all of the disk servers", but it might not be the best choice. Man page also says maxmbps is in the class of mmchconfig changes take place immediately.
We've only ever used QoS for throttling maint operations (restripes, etc) and are unfamiliar with how to best use it to throttle client load.

Best,
Chris

On 6/17/19, 12:40 PM, "gpfsug-discuss-bounces at spectrumscale.org on behalf of Skylar Thompson" <gpfsug-discuss-bounces at spectrumscale.org on behalf of skylar2 at uw.edu> wrote:

    IIRC, maxMBpS isn't really a limit, but more of a hint for how GPFS should
    use its in-memory buffers for read prefetches and dirty writes.

    On Mon, Jun 17, 2019 at 09:31:38AM -0700, Alex Chekholko wrote:
    > Hi Chris,
    >
    > I think the next thing to double-check is when the maxMBpS change takes
    > effect.  You may need to restart the nsds.  Otherwise I think your plan is
    > sound.
    >
    > Regards,
    > Alex
    >
    >
    > On Mon, Jun 17, 2019 at 9:24 AM Christopher Black <cblack at nygenome.org>
    > wrote:
    >
    > > Our network team sometimes needs to take down sections of our network for
    > > maintenance. Our systems have dual paths thru pairs of switches, but often
    > > the maintenance will take down one of the two paths leaving all our nsd
    > > servers with half bandwidth.
    > >
    > > Some of our systems are transmitting at a higher rate than can be handled
    > > by half network (2x40Gb hosts with tx of 50Gb+).
    > >
    > > What can we do to gracefully handle network maintenance reducing bandwidth
    > > in half?
    > >
    > > Should we set maxMBpS for affected nodes to a lower value? (default on our
    > > ess appears to be maxMBpS = 30000, would I reduce this to ~4000 for 32Gbps?)
    > >
    > > Any other ideas or comments?
    > >
    > > Our hope is that metadata operations are not affected much and users just
    > > see jobs and processes read or write at a slower rate.
    > >
    > >
    > >
    > > Best,
    > >
    > > Chris
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    --
    -- Skylar Thompson (skylar2 at u.washington.edu)
    -- Genome Sciences Department, System Administrator
    -- Foege Building S046, (206)-685-7354
    -- University of Washington School of Medicine
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