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From:   Song Liu <song@kernel.org>
Date:   Tue, 12 Oct 2021 01:17:43 -0700
Message-ID: <CAPhsuW4VFTpM94by-iMkTQ=b9Y7FqZ2oqHH+jV-f8BM=YKWyiA@mail.gmail.com>
Subject: Re: [PATCH RESEND] md: allow to set the fail_fast on RAID1/RAID10
To:     Li Feng <fengli@smartx.com>
Cc:     Xiao Ni <xni@redhat.com>,
        "open list:SOFTWARE RAID (Multiple Disks) SUPPORT" 
        <linux-raid@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Tue, Oct 12, 2021 at 1:07 AM Li Feng <fengli@smartx.com> wrote:
>
> Xiao Ni <xni@redhat.com> =E4=BA=8E2021=E5=B9=B410=E6=9C=8812=E6=97=A5=E5=
=91=A8=E4=BA=8C =E4=B8=8B=E5=8D=882:58=E5=86=99=E9=81=93=EF=BC=9A
> >
> > On Mon, Oct 11, 2021 at 5:42 PM Li Feng <fengli@smartx.com> wrote:
> > >
> > > Xiao Ni <xni@redhat.com> =E4=BA=8E2021=E5=B9=B410=E6=9C=8811=E6=97=A5=
=E5=91=A8=E4=B8=80 =E4=B8=8B=E5=8D=883:49=E5=86=99=E9=81=93=EF=BC=9A
> > > >
> > > > Hi all
> > > >
> > > > Now the per device sysfs interface file state can change failfast. =
Do
> > > > we need a new file for failfast?
> > > >
> > > > I did a test. The steps are:
> > > >
> > > > mdadm -CR /dev/md0 -l1 -n2 /dev/sdb /dev/sdc --assume-clean
> > > > cd /sys/block/md0/md/dev-sdb
> > > > echo failfast > state
> > > > cat state
> > > > in_sync,failfast
> > >
> > > This works,  will it be persisted to disk?
> > >
> >
> > mdadm --detail /dev/md0 can show the failfast information. So it
> > should be written in superblock.
> > But I don't find how md does this. I'm looking at this.
> >
> Yes, I have tested that it has been persisted, but don't understand who d=
oes it.

I think this is not guaranteed to be persistent:

[root@eth50-1 ~]# cat /sys/block/md127/md/rd1/state
in_sync,failfast
[root@eth50-1 ~]# echo -failfast >  /sys/block/md127/md/rd1/state
[root@eth50-1 ~]# cat /sys/block/md127/md/rd1/state
in_sync
[root@eth50-1 ~]# mdadm --stop /dev/md*
mdadm: /dev/md does not appear to be an md device
mdadm: stopped /dev/md127
[root@eth50-1 ~]# mdadm -As
mdadm: /dev/md/0_0 has been started with 4 drives.
[root@eth50-1 ~]# cat /sys/block/md127/md/rd1/state
in_sync,failfast

How about we fix state_store to make sure it is always persistent?

Thanks,
Song