RE: Backup Server RAID Array Event Notification

-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
owner@vger.kernel.org] On Behalf Of NeilBrown
Sent: Thursday, June 09, 2011 4:15 PM
To: lrhorer@satx.rr.com
Cc: 'Roman Mamedov'; linux-raid@vger.kernel.org
Subject: Re: Backup Server RAID Array Event Notification

On Thu, 9 Jun 2011 14:01:34 -0500 "Leslie Rhorer" [off-list ref]
wrote:

quoted

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-----Original Message-----
From: Roman Mamedov [mailto:rm@romanrm.ru]
Sent: Thursday, June 09, 2011 1:47 PM
To: lrhorer@satx.rr.com
Cc: linux-raid@vger.kernel.org
Subject: Re: Backup Server RAID Array Event Notification

On Thu, 9 Jun 2011 13:35:59 -0500
"Leslie Rhorer" [off-list ref] wrote:

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	After I created a pair of two member RAID1 arrays and then

added

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them as members to a RAID6 array, I am now getting messages similar

to

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the

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following, complaining of "Wrong-level" issues.  When I check the

RAID6

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array, however, it is clean and both RAID1 members are still there.

When I

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check both RAID1 arrays, they show clean with no events.  I am

running a

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compare between all the data on this machine and its mirror (this is

a

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backup machine).  So far everything looks good.  What does this

imply?

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Is

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there something about which I should be worried?

You said RAID1 twice, and your mdadm --detail doesn't agree with you

and

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says
"raid0" twice. Maybe you mistakenly used RAID1 instead of RAID0

somewhere

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else as well, and the WrongLevel message is trying to tell you that?

	No, that was just a typo.  (OK, three typos) I meant "RAID0".  The
RAID0 members are all 1T drives.  The RAID6 array is made of 1.5T

members.

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In order to use the 1T drives on the RAID6 array, I have to combine them
into 2T arrays, which then can be used as members of the RAID6 array.

If

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md10 and md11 were RAID1 arrays, they would only be 1T in extent, and

could

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not be members of md0.

"mdadm --monitor" does not monitor RAID0 or Linear arrays.  There is
nothing
to see.  Nothing can fail, they don't rebuilt, they are really just AID,
not
RAID.

	Well, OK.  So why does it report anything at all?

So if it thinks that it was asked to monitor a RAID0 it pretends that it
has
disappeared with reason "Wrong Level".
So if you explicitly ask it to monitor a RAID0, it won't and it will tell
you
why.

	That would make sense if I had started the monitor deamon and it had
sent the e-mail, but the monitor has been running for nearly two days, since
the system was rebooted.  Why send the message nearly a day after the deamon
is started, and why send it more than once (for each array)?

	By the same token, why did it wait nearly 8 hours and then again
more than a day and a half after the array was created to send the messages,
instead of immediately after it was created?

	This suggests I am going to be treated to a pair of spurious e-mails
every day or so telling me the device has disappeared, when it is perfectly
good.  After a few months of that, what happens when one of the devices
really does disappear?  We all know what happens to the system that cries,
"Wolf!" all the time.

If you only implicitly ask with e.g. "mdadm --monitor --scan" with a RAID0
listing in mdadm.conf it probably shouldn't give the message as it might
be confusing... but it does.

	I'm not sure I follow.

Or maybe the message is just confusing and I should change it.

Or something.

	Well that's definite.  :-)