And for raid1/raid10, it looks like fail_last_dev and FailFast want to
do opposite things.
It can fail the last and it doesn't send a rewrite bio when
fail_last_dev is true. Because the
last dev has been set faulty. There is no meaning to send the rewrite
bio. So FailFast only
works when fail_last_dev is false.
On Fri, Feb 11, 2022 at 2:48 PM Xiao Ni <xni@xxxxxxxxxx> wrote:
>
> Hi Marisuz
>
> We don't need to consider MD_FAILFAST for raid456. Because only raid1
> and raid10 support it.
> MD_FAILFAST_SUPPORTED is only set in raid1_run/raid10_run. So LastDev
> only be useful for
> raid1/raid10. It should be good to only check Faulty here.
>
> Best Regards
> Xiao
>
> On Wed, Feb 9, 2022 at 5:40 PM Mariusz Tkaczyk
> <mariusz.tkaczyk@xxxxxxxxxxxxxxx> wrote:
> >
> > Hi All,
> > During my work under failed arrays handling[1] improvements, I
> > discovered potential issue with "failfast" and metadata writes. In
> > commit message[2] Neil mentioned that:
> > "If we get a failure writing metadata but the device doesn't
> > fail, it must be the last device so we re-write without
> > FAILFAST".
> >
> > Obviously, this is not true for RAID456 (again)[1] but it is also not
> > true for RAID1 and RAID10 with "fail_las_dev"[3] functionality enabled.
> >
> > I did a quick check and can see that setter for "LastDev" flag is
> > called if "Faulty" on device is not set. I proposed some changes in the
> > area in my patchset[4] but after discussion we decided to drop changes
> > here. Current approach is not correct for all branches, so my proposal
> > is to change:
> >
> > diff --git a/drivers/md/md.c b/drivers/md/md.c
> > index 7b024912f1eb..3daec14ef6b2 100644
> > --- a/drivers/md/md.c
> > +++ b/drivers/md/md.c
> > @@ -931,7 +931,7 @@ static void super_written(struct bio *bio)
> > pr_err("md: %s gets error=%d\n", __func__,
> > blk_status_to_errno(bio->bi_status));
> > md_error(mddev, rdev);
> > - if (!test_bit(Faulty, &rdev->flags)
> > + if (test_bit(MD_BROKEN, mddev->flag)
> > && (bio->bi_opf & MD_FAILFAST)) {
> > set_bit(MD_SB_NEED_REWRITE, &mddev->sb_flags);
> > set_bit(LastDev, &rdev->flags);
> >
> >
> > It will force "LastDev" to be set on every metadata rewrite if mddevice
> > is known to be failed.
> > Do you have any other suggestions?
> >
> > + Guoqing - author of fail_last_dev.
> > + Xiao - you are familiarized with FailFast so please take a look.
> >
> > [1]https://lore.kernel.org/linux-raid/CAPhsuW54_9CTR6sh7mnQ6O77F2HNArLHGWHYsUdbNGy7pXgipQ@xxxxxxxxxxxxxx/T/#m8cf7c57429b6fd332220157186151900ce23865d
> > [2]https://git.kernel.org/pub/scm/linux/kernel/git/song/md.git/commit/?id=46533ff7fefb7e9e3539494f5873b00091caa8eb
> > [3]https://git.kernel.org/pub/scm/linux/kernel/git/song/md.git/commit/?id=9a567843f7ce
> > [4]https://lore.kernel.org/linux-raid/CAPhsuW5bV+Bz=Od9jomNHoedaEMFAXymN11J80G62GVPwSp41g@xxxxxxxxxxxxxx/
> >
> > Thanks,
> > Mariusz
> >
