Re: mdadm: failed devices become spares!

["Pierre Vignéras" <pierre@vigneras.name>]

On mercredi 19 mai 2010, MRK wrote:
> On 05/18/2010 04:06 AM, Neil Brown wrote:
> > However if --monitor gets to check the array between the above to events,
> > it will first see that the working drive is now faulty, so it reports a
> > failure, and then see that the faulty device isn't faulty any more and in
> > fact isn't even there.  The "isn't event there" bit doesn't register and
> > it treats it as 'SpareActive'.
> >
> > I should fix that.
> 
> However in one case the two events are not detected in the same round:
> 
> Apr 12 20:10:02 phobos mdadm[3157]: Fail event detected on md device
>  /dev/md2, component device /dev/sdf1
> Apr 12 20:11:02 phobos mdadm[3157]: SpareActive event detected on md device
> /dev/md2, component device /dev/sdf1
> 
> 
> 1 minute passes between the two entries. I suppose that's the mdadm
> daemon polling time.
> 
> In the other case all the entries are at the same time
> 
> Apr 13 08:00:02 phobos mdadm[3157]: Fail event detected on md device
>  /dev/md2, component device /dev/sdd1
> Apr 13 08:00:02 phobos mdadm[3157]: SpareActive event detected on md device
> /dev/md2, component device /dev/sdd1
> Apr 13 08:00:02 phobos last message repeated 7 times
> [...many times that messages..]
> 
> 
> ...plus, in this second case the SpareActive triggers a lot of times
> within that same second (Pierre you cut it short, but are all the "many
> times that messages" all at the exact same time or they span a few
>  seconds?)

Well I was probably  tired when I tried to filter the log for the bug report. 
It seems that this 'last message repeated 7 times' is for the:

Apr 13 08:00:02 phobos kernel: [5814019.208017] nfsd: non-standard errno: 5

not for the:

Apr 13 08:00:02 phobos mdadm[3157]: SpareActive event detected on md device 
/dev/md2, component device /dev/sdd1

I looked into my log and can't find something else. Sorry, sorry, sorry if 
this led you to false conclusions.

> It looks to me like some kind of usb failure where the USB connection or
> USB bridge momentarily fails then immediately gets re-detected and
> re-added to the system. But since there are no usb entries in dmesg,
> that would also be an issue of the usb driver. Could the problem also be
> a mixture with some unwise udev triggers of Debian, maybe somehow
> causing the auto-re-add of the drive to the RAID?
> 
> Pierre:
> - can you post your mdadm.conf?

Sure, but I am not sure it will be useful:

$ cat /etc/mdadm/mdadm.conf
# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays
ARRAY /dev/md0 level=raid1 num-devices=2 
UUID=13f4fdef:db0bd815:77e02d4f:1bda00b4
ARRAY /dev/md1 level=raid1 num-devices=2 
UUID=4a120782:2ed3053c:e99784b3:b8e5f7bf
ARRAY /dev/md4 level=raid1 num-devices=2 
UUID=b3c7212a:e95c5081:24bf28c1:396de87f
ARRAY /dev/md2 level=raid10 num-devices=4 
UUID=b34f4192:f823df58:24bf28c1:396de87f
ARRAY /dev/md3 level=raid5 num-devices=3 
UUID=e1f30f82:0999431b:24bf28c1:396de87f



> - USB is not good for RAID imho. Many times in my life I saw problems
> with USB/SATA bridges where the drive would get disconnected on high I/O
> activity and then reconnected after a few seconds. Anyway, readding it
> to the RAID shouldn't have happened. Also in my case there were "usb"
> entries in dmesg.

Well, that is what I discover: USB and RAID is not currently fine (hum, on 
Debian stable, not sure, we can say 'currently', kernel is:

$ uname -a
Linux phobos 2.6.26-2-686 #1 SMP Tue Mar 9 17:35:51 UTC 2010 i686 GNU/Linux
$

).

Anyway, it would be a great feature if USB can be used for a RAID setup, at 
least for end users (actually, I am using in my setup, a "special" layout for 
the using of RAID on several heterogeneous drives that I described here:

http://www.linuxconfig.org/prouhd-raid-for-the-end-user

)

Thanks for your help and regards.
-- 
Pierre Vignéras
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