The MD volume itself would not be unstable.   The filesystem,
directory and file structures could have been corrupted, likely it did
fix something that was not important enough to report.  When you hit
the specific directory entry and/or file data that would be when it
would crash.   I have no idea how many times I have fixed this sort of
issue, it is pretty common on an unexpected crash, maybe 1 in 10-50
crashes will produce this sort of error, the risk rises if files were
being created when it happens.

If you want to do a full test this will list out all dirs "find
/<dirname> -type f -ls" and this will actual read all files fairly
quickly.  If you want to check to see if all files and extents make
sense you can run the next commnad but it will take a long time
depending on how much data you have "find /<dirname> -type f -ls -exec
cksum {} \;"

On Sat, Jul 5, 2014 at 2:22 PM, Justin Stephenson
[off-list ref] wrote:

Hello Roger,

Thank-you for your email and for laying out some trouble shooting steps for
me. I will take these to heart and keep them on file for the future.

I can report that there was a screen of rapid scrolling text during the
crashes and some kind of memory contents dump that had a progress indicator.
From what I could see, there was some kind of kernel panic and a message
about ATA-9. Nothing in the /var/log/messages file as far as I could see.

I had tried unmounting and running fsck before but not with your specified
-f -y flags.

Here are the steps I took based on your input.

- ran system overnight with md raid unmounted.
- fully completed resync
- performed fsck -f -y. It took approx 6 minutes (on a 12TB volume). No
errors reported in the printout.
- reboot
- locally initiated and completed a 22 gb copy from and to the md raid and a
local esata external drive.

---

- from a workstation, opened SMB share to the MD raid
- workstation initiated copy to and from the CentOS box (and MD drive) of
the same 22gb folder over SMB.
- opened vnc client to the centOS box from a workstation.

Up until the fsck -f -y any of these three operations would cause a crash.


In summary, it would seem that the issue has been resolved by the fsck -f
-y. Up until running fsck - f -y, the system was completely unpredictable
when the MD drive was mounted - either during a sync or after it was
completed. I find this surprising, but perhaps I should not?

Based on Stan's email, I checked my UPS power settings, and I am certain I
was ending up with a hard powerdown when the battery ran out. I have
remedied this.

Could this have caused the MD volume to become unstable?

In any event, everything is up and running. I will report back with a log
entry if anything else appears.

Thanks again,

- Justin




------ Original Message ------
From: "Roger Heflin" <redacted>
To: "Justin Stephenson" <redacted>
Cc: stan@hardwarefreak.com; "Linux RAID" <redacted>
Sent: 05/07/2014 12:17:45 AM
Subject: Re: Re[2]: RAID 6 crashes system when being accessed

quoted

Some questions.

Do you get any messages on the screen when it crashes and/or is there
anything in /var/log/messages from the crashes?

Is a sync running when it crashes? If so what kind of SATA
controllers/setup are you using? I have had 2 previous setups that
would run fairly stably so long as a sync was not running, but if a
sync was running then the machine became unstable.

Did you umount it and run a "fsck -f -y" that took a while (at least
30 seconds) or just umount it and ran fsck and it finished quickly and
indicated clean? Generally if you nicely umount it the fs thinks it
is clean even when it is not because of some previous event.

On Fri, Jul 4, 2014 at 8:08 PM, Justin Stephenson
[off-list ref] wrote:

quoted

 Hi,

 Thanks for your reply.

 I should clarify that the crashes continue to be an issue in the absence
of
 any power outage so this issue is now independent of power. I mentioned
the
 UPS only with the thought that my problems may have been caused by a
sudden
 power-down.

 Please let me know if there are any logs or status print outs I could
pull
 to help troubleshoot this.

 Thanks Again,

 - J




 ------ Original Message ------
 From: "Stan Hoeppner" [off-list ref]
 To: "Justin Stephenson" [off-list ref];
 linux-raid@vger.kernel.org
 Sent: 04/07/2014 3:34:17 PM
 Subject: Re: RAID 6 crashes system when being accessed

quoted

 On 7/4/2014 9:11 AM, Justin Stephenson wrote:

quoted

  Hello,

  I am experiencing some issues with my md raid. It is crashing my
system
  when accessed with any "verve". The reboot initiates a resync of the
  raid. I have gone through the crash/reboot/resynced a number of times
  now and the crash happens within minutes of mounting the raid.

  Here are some details:

  - It is a raid 6 with 7 3TB devices.
  - Formatted as EXT4
  - mdadm v3.2.6 - 25th October 2012
  - centos 6.5 kernel 2.6.32-431.3.1.el6.x86_64
  - It has been running flawlessly for the previous 6 months.
  - I have a cron script running that resyncs monthly.
  - When the raid is unmounted, the system runs fine. (I have an
  additional "dumb" hardware raid 1 for dailies attached to an ESATA
port.
  This runs perfectly).
  - I am in the process of re-syncing the raid 6 again right now.
  - I have run an fsck on the raid volume after it was fully synced and
  everything came up clean.

  - there have been lots of power outages the last while with the hot
  summer in Toronto. My UPS shuts the system down for me, though I
think I
  can correlate the issues with the power outages.

 This sounds like the UPS is cutting power to the system before the
 shutdown sequence completes, before the array is stopped. This assumes
 you are already using apcupsd or similar. If you are check the
 configuration to make sure the system has plenty of time to shutdown
 after the UPS sends notification to the system. If you are not, then
 this will always happen as the UPS is simply cutting power when the
 battery gets low.

 Note that if the UPS is undersized for this system and only yields a
few
 minutes of on-battery time, it may simply not have enough juice to keep
 the machine up throughout the shutdown process.

 In summary, either your shutdown software isn't configured properly,
you
 are not using it, or the UPS is too small. This isn't an md problem.


 Cheers,

 Stan

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