Re: /dev/md0 can't be created

[Xiao Ni <xni@redhat.com>]

Hi Neil

   I think that is enough to say it's not the problem about md. I really be
thankful for you about the analysis.

Best Regards
Xiao

----- Original Message -----
> From: "NeilBrown" <neilb@suse.de>
> To: "Xiao Ni" <xni@redhat.com>
> Cc: linux-raid@vger.kernel.org
> Sent: Wednesday, April 1, 2015 10:53:21 AM
> Subject: Re: /dev/md0 can't be created
> 
> On Fri, 27 Mar 2015 02:06:21 -0400 (EDT) Xiao Ni <xni@redhat.com> wrote:
> 
> > 
> >   I'm lucky, I reproduced it again and I ran the command udevadm monitor >
> >   monitor before test.
> > I'll put it in as an attachment.
> > 
> >   I found there is a not whole message in the last line.
> > 
> > Xiao
> 
> The line:
> 
>  UDEV  [7083.531441] add      /devices/virtual/block/md0 (block)
> 
> confirms that udev saw an 'add' event for /dev/md0.
> 
> That should be enough for udev to create the device node.
> If it doesn't, you need to look into udev and find out why it doesn't.
> I can't really help you there - I don't find udev very easy to debug.
> 
> NeilBrown
> 
> 
> > 
> > ----- Original Message -----
> > > From: "Xiao Ni" <xni@redhat.com>
> > > To: "NeilBrown" <neilb@suse.de>
> > > Cc: linux-raid@vger.kernel.org
> > > Sent: Thursday, March 26, 2015 3:36:35 PM
> > > Subject: Re: /dev/md0 can't be created
> > > 
> > > Hi Neil
> > > 
> > >    I can reproduce it now. Do you want me to run udevadm monitor before
> > >    the
> > >    test?
> > > And I checked the /var/log/messages, it show the information:
> > > 
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-2>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-3>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-4>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-5>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-6>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-7>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-9>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: bind<dm-8>
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-7 operational
> > > as
> > > raid disk 5
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-6 operational
> > > as
> > > raid disk 4
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-5 operational
> > > as
> > > raid disk 3
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-4 operational
> > > as
> > > raid disk 2
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-3 operational
> > > as
> > > raid disk 1
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: device dm-2 operational
> > > as
> > > raid disk 0
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: allocated 0kB
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid:md0: raid level 5 active with
> > > 6
> > > out of 7 devices, algorithm 2
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md/raid456: discard support disabled
> > > due
> > > to uncertainty.
> > > Oct 20 19:59:59 ibm-z10-25 kernel: Set
> > > raid456.devices_handle_discard_safely=Y to override.
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md0: detected capacity change from 0
> > > to
> > > 1881145344
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: recovery of RAID array md0
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: minimum _guaranteed_  speed: 1000
> > > KB/sec/disk.
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: using maximum available idle IO
> > > bandwidth (but not more than 200000 KB/sec) for recovery.
> > > Oct 20 19:59:59 ibm-z10-25 kernel: md: using 128k window, over a total of
> > > 306176k.
> > > Oct 20 19:59:59 ibm-z10-25 systemd-udevd: inotify_add_watch(7, /dev/md0,
> > > 10)
> > > failed: No such file or directory
> > >   
> > > Xiao
> > > 
> > > ----- Original Message -----
> > > > From: "NeilBrown" <neilb@suse.de>
> > > > To: "Xiao Ni" <xni@redhat.com>
> > > > Cc: linux-raid@vger.kernel.org
> > > > Sent: Wednesday, March 25, 2015 2:35:29 PM
> > > > Subject: Re: /dev/md0 can't be created
> > > > 
> > > > On Wed, 25 Mar 2015 02:15:34 -0400 (EDT) Xiao Ni <xni@redhat.com>
> > > > wrote:
> > > > 
> > > > > Hi all
> > > > > 
> > > > >    I have encountered so many times, the raid device is created
> > > > >    successfully, but the directory
> > > > > /dev/md0 can't be created. It can't reproduce 100%.
> > > > > 
> > > > > [root@intel-sugarbay-do-01 create_assemble]# cat /proc/mdstat
> > > > > Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
> > > > > md0 : active raid10 loop7[7](S) loop6[6] loop5[5] loop4[4] loop3[3]
> > > > > loop2[2] loop1[1] loop0[0]
> > > > >       1788416 blocks super 1.2 512K chunks 2 near-copies [7/7]
> > > > >       [UUUUUUU]
> > > > >       bitmap: 0/1 pages [0KB], 65536KB chunk
> > > > > 
> > > > > unused devices: <none>
> > > > > [root@intel-sugarbay-do-01 create_assemble]# ls /dev/md0
> > > > > ls: cannot access /dev/md0: No such file or directory
> > > > > 
> > > > >     The underline devices are loop devices which are created with big
> > > > >     file.
> > > > > 
> > > > >     The kernel I used is RHEL7 (3.10.0-234.el7.x86_64.debug, mdadm -
> > > > >     v3.3.2
> > > > >     - 21st August 2014)
> > > > > I'll try to reproduce this with upstream kernel and mdadm. But I
> > > > > think it
> > > > > shouldn't be the problem about kernel.
> > > > > 
> > > > >     What do you think I should check for this? And which tool is
> > > > >     responsible for creating the directory? Maybe
> > > > > I can add some log to it to find the reason.
> > > > > 
> > > > 
> > > > /dev/md0 is created by udev.
> > > > Run
> > > >   udevadm monitor
> > > > 
> > > > to see the events that udev is processing.  When and ADD event for
> > > > "md0" is
> > > > processed, /dev/md0 should get created.
> > > > 
> > > > NeilBrown
> > > > 
> > > --
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> > > 
> 
>