[dm-devel] deterministic io throughput in multipath

[Benjamin Marzinski]

On Mon, Dec 26, 2016 at 09:42:48AM +0000, Muneendra Kumar M wrote:
> Hi Ben,
> 
> If there are two paths on a dm-1 say sda and sdb as below.
> 
> #  multipath -ll
> 	mpathd (3600110d001ee7f0102050001cc0b6751) dm-1 SANBlaze,VLUN MyLun
> 	size=8.0M features='0' hwhandler='0' wp=rw
> 	`-+- policy='round-robin 0' prio=50 status=active
> 	  |- 8:0:1:0  sda 8:48 active ready  running
> 	  `- 9:0:1:0  sdb 8:64 active ready  running          
> 
> And on sda if iam seeing lot of errors due to which the sda path is fluctuating from failed state to active state and vicevera.
> 
> My requirement is something like this if sda is failed for more then 5 times in a hour duration ,then I want to keep the sda in failed state for few hours (3hrs)
> 
> And the data should travel only thorugh sdb path.
> Will this be possible with the below parameters.

No. delay_watch_checks sets how may path checks you watch a path that
has recently come back from the failed state. If the path fails again
within this time, multipath device delays it.  This means that the delay
is always trigger by two failures within the time limit.  It's possible
to adapt this to count numbers of failures, and act after a certain
number within a certain timeframe, but it would take a bit more work.

delay_wait_checks doesn't guarantee that it will delay for any set
length of time.  Instead, it sets the number of consecutive successful
path checks that must occur before the path is usable again. You could
set this for 3 hours of path checks, but if a check failed during this
time, you would restart the 3 hours over again.

-Ben

> Can you just let me know what values I should add for delay_watch_checks and delay_wait_checks.
> 
> Regards,
> Muneendra.
> 
> 
> 
> -----Original Message-----
> From: Muneendra Kumar M 
> Sent: Thursday, December 22, 2016 11:10 AM
> To: 'Benjamin Marzinski' <bmarzins at redhat.com>
> Cc: dm-devel at redhat.com
> Subject: RE: [dm-devel] deterministic io throughput in multipath
> 
> Hi Ben,
> 
> Thanks for the reply.
> I will look into this parameters will do the internal testing and let you know the results.
> 
> Regards,
> Muneendra.
> 
> -----Original Message-----
> From: Benjamin Marzinski [mailto:bmarzins at redhat.com] 
> Sent: Wednesday, December 21, 2016 9:40 PM
> To: Muneendra Kumar M <mmandala at Brocade.com>
> Cc: dm-devel at redhat.com
> Subject: Re: [dm-devel] deterministic io throughput in multipath
> 
> Have you looked into the delay_watch_checks and delay_wait_checks configuration parameters?  The idea behind them is to minimize the use of paths that are intermittently failing.
> 
> -Ben
> 
> On Mon, Dec 19, 2016 at 11:50:36AM +0000, Muneendra Kumar M wrote:
> >    Customers using Linux host (mostly RHEL host) using a SAN network for
> >    block storage, complain the Linux multipath stack is not resilient to
> >    handle non-deterministic storage network behaviors. This has caused many
> >    customer move away to non-linux based servers. The intent of the below
> >    patch and the prevailing issues are given below. With the below design we
> >    are seeing the Linux multipath stack becoming resilient to such network
> >    issues. We hope by getting this patch accepted will help in more Linux
> >    server adoption that use SAN network.
> > 
> >    I have already sent the design details to the community in a different
> >    mail chain and the details are available in the below link.
> > 
> >    [1]https://urldefense.proofpoint.com/v2/url?u=https-3A__www.redhat.com_archives_dm-2Ddevel_2016-2DDecember_msg00122.html&d=DgIDAw&c=IL_XqQWOjubgfqINi2jTzg&r=E3ftc47B6BGtZ4fVaYvkuv19wKvC_Mc6nhXaA1sBIP0&m=vfwpVp6e1KXtRA0ctwHYJ7cDmPsLi2C1L9pox7uexsY&s=q5OI-lfefNC2CHKmyUkokgiyiPo_Uj7MRu52hG3MKzM&e= .
> > 
> >    Can you please go through the design and send the comments to us.
> > 
> >     
> > 
> >    Regards,
> > 
> >    Muneendra.
> > 
> >     
> > 
> >     
> > 
> > References
> > 
> >    Visible links
> >    1. 
> > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.redhat.com_ar
> > chives_dm-2Ddevel_2016-2DDecember_msg00122.html&d=DgIDAw&c=IL_XqQWOjub
> > gfqINi2jTzg&r=E3ftc47B6BGtZ4fVaYvkuv19wKvC_Mc6nhXaA1sBIP0&m=vfwpVp6e1K
> > XtRA0ctwHYJ7cDmPsLi2C1L9pox7uexsY&s=q5OI-lfefNC2CHKmyUkokgiyiPo_Uj7MRu
> > 52hG3MKzM&e=
> 
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