BUG:write data to degrade raid5

BUG:write data to degrade raid5

[jin zhencheng]

hi;

i use kernel is 2.6.26.2

what i do as follow:

1, I create a raid5:
mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
--metadata=1.0 --assume-clean

2, dd if=/dev/zero of=/dev/md5 bs=1M &

write data to this raid5

3, mdadm --manage /dev/md5 -f /dev/sda

4 mdadm --manage  /dev/md5 -f /dev/sdb

if i faild 2 disks ,then the OS kernel display OOP error and kernel down


do somebody know why ?

Is MD/RAID5 bug ?

Re: BUG:write data to degrade raid5

[Joachim Otahal]

jin zhencheng schrieb:
> hi;
>
> i use kernel is 2.6.26.2
>
> what i do as follow:
>
> 1, I create a raid5:
> mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
> --metadata=1.0 --assume-clean
>
> 2, dd if=/dev/zero of=/dev/md5 bs=1M&
>
> write data to this raid5
>
> 3, mdadm --manage /dev/md5 -f /dev/sda
>
> 4 mdadm --manage  /dev/md5 -f /dev/sdb
>
> if i faild 2 disks ,then the OS kernel display OOP error and kernel down
>
> do somebody know why ?
>
> Is MD/RAID5 bug ?
>    

RAID5 can only tolerate ONE drive to fail of ALL members. If you want to 
be able to fail two drives you will have to use RAID6 or RAID5 with one 
hot-spare (and give it time to rebuild before failing the second drive).
PLEASE read the documentation on raid levels, like on wikipedia.

Joachim Otahal

Re: BUG:write data to degrade raid5

[Robin Hill]

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On Fri Mar 19, 2010 at 07:20:42PM +0100, Joachim Otahal wrote:

> jin zhencheng schrieb:
> > hi;
> >
> > i use kernel is 2.6.26.2
> >
> > what i do as follow:
> >
> > 1, I create a raid5:
> > mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
> > --metadata=1.0 --assume-clean
> >
> > 2, dd if=/dev/zero of=/dev/md5 bs=1M&
> >
> > write data to this raid5
> >
> > 3, mdadm --manage /dev/md5 -f /dev/sda
> >
> > 4 mdadm --manage  /dev/md5 -f /dev/sdb
> >
> > if i faild 2 disks ,then the OS kernel display OOP error and kernel down
> >
> > do somebody know why ?
> >
> > Is MD/RAID5 bug ?
> >    
> 
> RAID5 can only tolerate ONE drive to fail of ALL members. If you want to 
> be able to fail two drives you will have to use RAID6 or RAID5 with one 
> hot-spare (and give it time to rebuild before failing the second drive).
> PLEASE read the documentation on raid levels, like on wikipedia.
> 
Yes, but the kernel should _not_ OOPS if two drives fail.  However,
given that the kernel version used is 18 months old, I'm not sure the
bug report is particularly useful.  If it's a distro-specific kernel
then report the issue to them, otherwise try installing a more recent
kernel release.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <robin@robinhill.me.uk> |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |

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Re: BUG:write data to degrade raid5

[Kristleifur Daðason]

On Fri, Mar 19, 2010 at 6:20 PM, Joachim Otahal <Jou@gmx.net> wrote:
> jin zhencheng schrieb:
>>
>> hi;
>>
>> i use kernel is 2.6.26.2
>>
>> what i do as follow:
>>
>> 1, I create a raid5:
>> mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
>> --metadata=1.0 --assume-clean
>>
>> 2, dd if=/dev/zero of=/dev/md5 bs=1M&
>>
>> write data to this raid5
>>
>> 3, mdadm --manage /dev/md5 -f /dev/sda
>>
>> 4 mdadm --manage  /dev/md5 -f /dev/sdb
>>
>> if i faild 2 disks ,then the OS kernel display OOP error and kernel down
>>
>> do somebody know why ?
>>
>> Is MD/RAID5 bug ?
>>
>
> RAID5 can only tolerate ONE drive to fail of ALL members. If you want to be
> able to fail two drives you will have to use RAID6 or RAID5 with one
> hot-spare (and give it time to rebuild before failing the second drive).
> PLEASE read the documentation on raid levels, like on wikipedia.
>

That is true,

but should we get a kernel oops and crash if two RAID5 drives are
failed? (THAT part looks like a bug!)

Jin, can you try a newer kernel, and a newer mdadm?

-- Kristleifur
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Re: BUG:write data to degrade raid5

[Joachim Otahal]

Kristleifur Daðason schrieb:
> On Fri, Mar 19, 2010 at 6:20 PM, Joachim Otahal <Jou@gmx.net 
> <mailto:Jou@gmx.net>> wrote:
>
>     jin zhencheng schrieb:
>
>         hi;
>
>         i use kernel is 2.6.26.2
>
>         what i do as follow:
>
>         1, I create a raid5:
>         mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
>         --metadata=1.0 --assume-clean
>
>         2, dd if=/dev/zero of=/dev/md5 bs=1M&
>
>         write data to this raid5
>
>         3, mdadm --manage /dev/md5 -f /dev/sda
>
>         4 mdadm --manage  /dev/md5 -f /dev/sdb
>
>         if i faild 2 disks ,then the OS kernel display OOP error and
>         kernel down
>
>         do somebody know why ?
>
>         Is MD/RAID5 bug ?
>
>
>     RAID5 can only tolerate ONE drive to fail of ALL members. If you
>     want to be able to fail two drives you will have to use RAID6 or
>     RAID5 with one hot-spare (and give it time to rebuild before
>     failing the second drive).
>     PLEASE read the documentation on raid levels, like on wikipedia.
>
>
> That is true,
>
> but should we get a kernel oops and crash if two RAID5 drives are 
> failed? (THAT part looks like a bug!)
>
> Jin, can you try a newer kernel, and a newer mdadm?
>
> -- Kristleifur
You are probably right.
My kernel version is "Debian 2.6.26-21lenny4", and I had no oopses 
during my hot-plug testing one the hardware I use md on. I think it may 
be the driver for his chips.

Jin:

Did you really use the whole drives for testing or loopback files or 
partitions on the drives? I never did my hot-plug testings with whole 
drives being in an array, only with partitions.

Joachim Otahal

Re: BUG:write data to degrade raid5

[jin zhencheng]

hi Joachim Otahal:

ths for your test on "Debian 2.6.26-21lenny4".
if you want to see the oop ,you should always write to the raid5 ,and
pull 2 disks out.maybe you can see the error

i think no matter what i do ,even if i pull out all the disk , kernel
should not oop.


On Sat, Mar 20, 2010 at 2:37 AM, Joachim Otahal <Jou@gmx.net> wrote:
> Kristleifur Dağason schrieb:
>>
>> On Fri, Mar 19, 2010 at 6:20 PM, Joachim Otahal <Jou@gmx.net
>> <mailto:Jou@gmx.net>> wrote:
>>
>>    jin zhencheng schrieb:
>>
>>        hi;
>>
>>        i use kernel is 2.6.26.2
>>
>>        what i do as follow:
>>
>>        1, I create a raid5:
>>        mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
>>        --metadata=1.0 --assume-clean
>>
>>        2, dd if=/dev/zero of=/dev/md5 bs=1M&
>>
>>        write data to this raid5
>>
>>        3, mdadm --manage /dev/md5 -f /dev/sda
>>
>>        4 mdadm --manage  /dev/md5 -f /dev/sdb
>>
>>        if i faild 2 disks ,then the OS kernel display OOP error and
>>        kernel down
>>
>>        do somebody know why ?
>>
>>        Is MD/RAID5 bug ?
>>
>>
>>    RAID5 can only tolerate ONE drive to fail of ALL members. If you
>>    want to be able to fail two drives you will have to use RAID6 or
>>    RAID5 with one hot-spare (and give it time to rebuild before
>>    failing the second drive).
>>    PLEASE read the documentation on raid levels, like on wikipedia.
>>
>>
>> That is true,
>>
>> but should we get a kernel oops and crash if two RAID5 drives are failed?
>> (THAT part looks like a bug!)
>>
>> Jin, can you try a newer kernel, and a newer mdadm?
>>
>> -- Kristleifur
>
> You are probably right.
> My kernel version is "Debian 2.6.26-21lenny4", and I had no oopses during my
> hot-plug testing one the hardware I use md on. I think it may be the driver
> for his chips.
>
> Jin:
>
> Did you really use the whole drives for testing or loopback files or
> partitions on the drives? I never did my hot-plug testings with whole drives
> being in an array, only with partitions.
>
> Joachim Otahal
>
>

Re: BUG:write data to degrade raid5

[Henrique de Moraes Holschuh]

On Sun, 21 Mar 2010, jin zhencheng wrote:
> ths for your test on "Debian 2.6.26-21lenny4".
> if you want to see the oop ,you should always write to the raid5 ,and
> pull 2 disks out.maybe you can see the error
> 
> i think no matter what i do ,even if i pull out all the disk , kernel
> should not oop.

You don't have swap (file or partition, doesn't matter) on that RAID, do
you?

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: BUG:write data to degrade raid5

[jin zhencheng]

don't have swap on the RAID.

On Sun, Mar 21, 2010 at 9:04 PM, Henrique de Moraes Holschuh
<hmh@hmh.eng.br> wrote:
> On Sun, 21 Mar 2010, jin zhencheng wrote:
>> ths for your test on "Debian 2.6.26-21lenny4".
>> if you want to see the oop ,you should always write to the raid5 ,and
>> pull 2 disks out.maybe you can see the error
>>
>> i think no matter what i do ,even if i pull out all the disk , kernel
>> should not oop.
>
> You don't have swap (file or partition, doesn't matter) on that RAID, do
> you?
>
> --
>  "One disk to rule them all, One disk to find them. One disk to bring
>  them all and in the darkness grind them. In the Land of Redmond
>  where the shadows lie." -- The Silicon Valley Tarot
>  Henrique Holschuh
>

Re: BUG:write data to degrade raid5

[Bill Davidsen]

jin zhencheng wrote:
> hi;
>
> i use kernel is 2.6.26.2
>
> what i do as follow:
>
> 1, I create a raid5:
> mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
> --metadata=1.0 --assume-clean
>
> 2, dd if=/dev/zero of=/dev/md5 bs=1M &
>
> write data to this raid5
>
> 3, mdadm --manage /dev/md5 -f /dev/sda
>
> 4 mdadm --manage  /dev/md5 -f /dev/sdb
>
> if i faild 2 disks ,then the OS kernel display OOP error and kernel down
>
>
> do somebody know why ?
>
> Is MD/RAID5 bug ?
>   

I would usually say that any kernel OOPS is a bug, but in this case, 
what are you running your Linux on, given that you just trashed the 
first four drives? While it's possible to run off of other drives, you 
have to make an effort to configure Linux to do so.

-- 
Bill Davidsen <davidsen@tmr.com>
  "We can't solve today's problems by using the same thinking we
   used in creating them." - Einstein

Re: BUG:write data to degrade raid5

[Neil Brown]

On Fri, 19 Mar 2010 18:29:28 +0800
jin zhencheng <zhenchengjin@gmail.com> wrote:

> hi;
> 
> i use kernel is 2.6.26.2
> 
> what i do as follow:
> 
> 1, I create a raid5:
> mdadm -C /dev/md5 -l 5 -n 4 /dev/sda /dev/sdb /dev/sdc  /dev/sdd
> --metadata=1.0 --assume-clean
> 
> 2, dd if=/dev/zero of=/dev/md5 bs=1M &
> 
> write data to this raid5
> 
> 3, mdadm --manage /dev/md5 -f /dev/sda
> 
> 4 mdadm --manage  /dev/md5 -f /dev/sdb
> 
> if i faild 2 disks ,then the OS kernel display OOP error and kernel down
> 
> 
> do somebody know why ?
> 
> Is MD/RAID5 bug ?

Certainly this is a bug.
2.6.26 is quite old now - it is possible that the bug has already been fixed.
If you are able to post the oops message - possibly use a digital camera to
get a photograph - then I can probably explain what is happening and whether
it has been fixed.

Thanks,
NeilBrown