On Tue, Mar 01, 2016 at 05:50:09PM -0700, rodman@shellport.com wrote:

It appears this is not an Mdadm bug but is in fact kernel/dash issue as
you noted, Piergiorgio.

quoted

From the bug tracker here: 

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787950

"This is a kernel/dash issue. In kernel 4.0, the md sysfs implementation
does not work with partial reads from /sys/block/md0/md/sync_action;
the read syscall returns the entire contents of the file even if you
try to read less. Dash has an inefficient implementation which reads
input one byte at a time, and fails when it hits the kernel
misbehavior."

Just tested:

dd if=/sys/block/md0/md/sync_action bs=1 count=1

On kernel 3.x I get "i", on kernel 4.x I get "idle"... :-)

The work around is what you said.  Substitute bash for sh at the
beginning of the script.  Unfortunately that doesn't work for me as I
get this error when trying to run checkarray now:
"checkarray: E: /sys/block/md0/md/sync_action not writeable."

Well, first check the permissions with:

ls -l /sys/block/md0/md/sync_action

Then make sure you're root, otherwise it will
not be possible to write, of course.

bye,

pg

I'll do some research to see what's that's about.  I'm glad to know its
not a Mdadm issue per say.

Rodman Frowert

-------- Original Message --------
Subject: Re: Checkarray doesn't seem to do anything
From: Piergiorgio Sartor <redacted>
Date: Tue, March 01, 2016 4:25 pm
To: rodman@shellport.com
Cc: linux-raid@vger.kernel.org

On Tue, Mar 01, 2016 at 02:57:21PM -0700, rodman@shellport.com wrote:

quoted

Thank you for that information. My kernel is 4.2.0.

I guess the problem is the same.

quoted

Is this it's intended behavior or is it simply a bug that has not been
corrected?

Well, I think it is a bug.
I'm not sure if "dash" bug or kernel bug.
I suspect "dash", since "bash" works...

quoted

I only bring this up as nearly all mdadm config tutorials at some point
mention the checkarray function. They also point out that checkarray is
also auto configured in the cron tab (cron.d) to run once a month. But
of course, if checkarray doesn't work then people may think it is
running once a month when it really isn't.

Exactly!
I've some Ubuntu 14.04.x with old kernel, and one
with new kernel.
This one has a "weak" HDD in RAID (one / some blocks
waiting for relocation).
In my sytems the check occurs weekly, but it did not!
Tried from command line to no avail...
Debugging the script led to the previous result.

I'm not sure, maybe someone should file a bug, but I
have not to much faith in Ubuntu md/mdadm support.
In the past they were slow or no reacting, and "mdadm"
was always an obsolete version (like it is in 14.04.x).
Maybe Debian could be a better place, not sure.

bye,

pg

quoted

Rodman Frowert -------- Original Message --------
Subject: Re: Checkarray doesn't seem to do anything
From: Piergiorgio Sartor <redacted>
Date: Tue, March 01, 2016 3:33 pm
To: rodman@shellport.com
Cc: linux-raid@vger.kernel.org

On Tue, Mar 01, 2016 at 02:09:44PM -0700, rodman@shellport.com wrote:

quoted

Hello,

I have a question as it pertains to the checkarray function of Mdadm.

I

quoted

can't actually get it to do anything. I'm running Ubuntu 14.04.4

Server

quoted

LTS with the latest mdadm installed. I have a single RAID 1 mirror
configured and working properly near as I can tell. 

I can force a check if I issue "echo check >
/sys/block/md0/md/sync_action" as root. I can then see the status of
the check via /proc/mdstat or using the --detail switch on mdadm

itself.

quoted

However, nothing happens if I type in:
/usr/share/mdadm/checkarray -a
or
/usr/share/mdadm/checkarray -a /dev/mdX
or
/usr/share/mdadm/checkarray -as

I've tried the commands as root and using sudo. The array sits idle
after all of the above commands. The only thing I can actually get
checkarray to perform is to give me the help output if I pass it -h.

I

quoted

have attached, below, the current status of the mdadm managed array. 
Doing some Googling I haven't been able to find anyone else that

isn't

quoted

able to use the checkarray function so I must be doing something

wrong.

quoted

Any ideas?

Well, yes, I've the same problem.

Ubuntu 14.04.x with kernel 3.13, "checkarray" works.
Ubuntu 14.04.x with kernel 4.11 (I think), "checkarray"
does not work.

The script runs with "dash" (not "bash") and it has
a "read cur_status < something_from_sysfs" in order to check
the array status.
With kernel 3.13, the "read" returns the proper value,
with kernel 4.11 (I think) the very same "read" exits
the script without any message or else.

One option is to use "bash", that is change the top
of the script from: #!/bin/sh to #!/bin/bash

Another is to change the "read", with a "cat", that is
something like: cur_status=$( cat something_from_sysfs )

You can check yourself, there is only one "read" in
the script (if I recall correctly).

Hope this helps,

bye,

pg

quoted

Rodman Frowert

quoted

cat /proc/mdstat shows:
------------------
rodman@nas:/usr/share/mdadm$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5]
[raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
5860389696 blocks super 1.2 [2/2] [UU]
-----------------

sudo mdadm --detail /dev/md0 shows:
------------------
rodman@nas:/usr/share/mdadm$ sudo mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Feb 26 14:07:40 2016
Raid Level : raid1
Array Size : 5860389696 (5588.90 GiB 6001.04 GB)
Used Dev Size : 5860389696 (5588.90 GiB 6001.04 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Tue Mar 1 07:40:19 2016
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Name : nas:0 (local to host nas)
UUID : 4765e7df:0e1a6ad2:1321765f:a2d9f2c9
Events : 164

Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1

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