manually destriping a 4 drive raid5 with one missing drive

manually destriping a 4 drive raid5 with one missing drive

[Marek]

hi,

i'd like to ask whether manual  destriping of a 4 drive raid5 is
possible even though the parity information is lost due to forced
resync of all four drives.

Marek

Re: manually destriping a 4 drive raid5 with one missing drive

[Neil Brown]

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Marek <mlf.conv@gmail.com> writes:

> hi,
>
> i'd like to ask whether manual  destriping of a 4 drive raid5 is
> possible even though the parity information is lost due to forced
> resync of all four drives.
>

I'm sorry but I have no idea what you are asking.
Maybe if you provided more details about your current circumstances, how
you got into that situation, and what outcome you are hoping for, then I
might be able to help.

NeilBrown

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Fwd: manually destriping a 4 drive raid5 with one missing drive

[Marek]

I have a 4 2TB disk  raid5 512k 1.2.
one of the drives was accidentally wiped by ubuntu installation
(/dev/sda, first drive). The system has been rebooted forcefully
several times before this happened. Raid wouldn't come up after that.
The first drive has been -add ed back and a resync has been enforced.
What i'd like to do is to manually destrip the raid.

On Sun, Oct 18, 2015 at 12:54 AM, Neil Brown <nfbrown@novell.com> wrote:
> Marek <mlf.conv@gmail.com> writes:
>
>> hi,
>>
>> i'd like to ask whether manual  destriping of a 4 drive raid5 is
>> possible even though the parity information is lost due to forced
>> resync of all four drives.
>>
>
> I'm sorry but I have no idea what you are asking.
> Maybe if you provided more details about your current circumstances, how
> you got into that situation, and what outcome you are hoping for, then I
> might be able to help.
>
> NeilBrown

Re: manually destriping a 4 drive raid5 with one missing drive

[Alexander Afonyashin]

Hi Marek,

First, check status of disk you would like to remove via:
- cat /proc/mdstat
- mdadm -D /dev/md0 (replace md0 with you md-raid identifier)

Regards,
Alexader

On Fri, Oct 23, 2015 at 12:26 PM, Marek <mlf.conv@gmail.com> wrote:
> I have a 4 2TB disk  raid5 512k 1.2.
> one of the drives was accidentally wiped by ubuntu installation
> (/dev/sda, first drive). The system has been rebooted forcefully
> several times before this happened. Raid wouldn't come up after that.
> The first drive has been -add ed back and a resync has been enforced.
> What i'd like to do is to manually destrip the raid.
>
> On Sun, Oct 18, 2015 at 12:54 AM, Neil Brown <nfbrown@novell.com> wrote:
>> Marek <mlf.conv@gmail.com> writes:
>>
>>> hi,
>>>
>>> i'd like to ask whether manual  destriping of a 4 drive raid5 is
>>> possible even though the parity information is lost due to forced
>>> resync of all four drives.
>>>
>>
>> I'm sorry but I have no idea what you are asking.
>> Maybe if you provided more details about your current circumstances, how
>> you got into that situation, and what outcome you are hoping for, then I
>> might be able to help.
>>
>> NeilBrown
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Re: manually destriping a 4 drive raid5 with one missing drive

[Piergiorgio Sartor]

On Fri, Oct 23, 2015 at 11:26:12AM +0200, Marek wrote:
> I have a 4 2TB disk  raid5 512k 1.2.
> one of the drives was accidentally wiped by ubuntu installation
> (/dev/sda, first drive). The system has been rebooted forcefully
> several times before this happened. Raid wouldn't come up after that.
> The first drive has been -add ed back and a resync has been enforced.
> What i'd like to do is to manually destrip the raid.

Hi Marek,

excuse my ignorance, but what does it mean "destrip" a RAID?

Could you please point to some technical reference or, maybe,
spend few more words to clarify the concept?

Thanks,

bye,

-- 

piergiorgio

Fwd: manually destriping a 4 drive raid5 with one missing drive

[Marek]

Not sure if it's destrip or destripe but it's basically like puzzle
you take a block from each drive according to the layout you are using
e.g. Left symmetric and then write it down in that order computing
missing blocks from parity blocks - this way you would write an image
which you can mount without using mdadm. Data restoration companies
are using this technique.


On Friday, October 23, 2015, Piergiorgio Sartor
<piergiorgio.sartor@nexgo.de> wrote:
>
> On Fri, Oct 23, 2015 at 11:26:12AM +0200, Marek wrote:
> > I have a 4 2TB disk  raid5 512k 1.2.
> > one of the drives was accidentally wiped by ubuntu installation
> > (/dev/sda, first drive). The system has been rebooted forcefully
> > several times before this happened. Raid wouldn't come up after that.
> > The first drive has been -add ed back and a resync has been enforced.
> > What i'd like to do is to manually destrip the raid.
>
> Hi Marek,
>
> excuse my ignorance, but what does it mean "destrip" a RAID?
>
> Could you please point to some technical reference or, maybe,
> spend few more words to clarify the concept?
>
> Thanks,
>
> bye,
>
> --
>
> piergiorgio

Re: Fwd: manually destriping a 4 drive raid5 with one missing drive

[Phil Turmel]

On 10/23/2015 12:20 PM, Marek wrote:
> Not sure if it's destrip or destripe but it's basically like puzzle
> you take a block from each drive according to the layout you are using
> e.g. Left symmetric and then write it down in that order computing
> missing blocks from parity blocks - this way you would write an image
> which you can mount without using mdadm. Data restoration companies
> are using this technique.

No special tool required.  Obtain a new drive big enough to hold your
entire array and 'dd' from /dev/mdX to your new drive.

{ BTW: convention on kernel.org is to reply-to-all, trim unnecessary
context, and either bottom post or interleave your reply. }

Phil

Re: Fwd: manually destriping a 4 drive raid5 with one missing drive

[Marek]

dd from mdX doesn't work i tried it even with testdisk, what you get
is mixed up data, incomplete files.

{ Google mail on iPad doesn't support plain text, who knew :/ }

On Fri, Oct 23, 2015 at 7:49 PM, Phil Turmel <philip@turmel.org> wrote:
> On 10/23/2015 12:20 PM, Marek wrote:
>> Not sure if it's destrip or destripe but it's basically like puzzle
>> you take a block from each drive according to the layout you are using
>> e.g. Left symmetric and then write it down in that order computing
>> missing blocks from parity blocks - this way you would write an image
>> which you can mount without using mdadm. Data restoration companies
>> are using this technique.
>
> No special tool required.  Obtain a new drive big enough to hold your
> entire array and 'dd' from /dev/mdX to your new drive.
>
> { BTW: convention on kernel.org is to reply-to-all, trim unnecessary
> context, and either bottom post or interleave your reply. }
>
> Phil

Re: Fwd: manually destriping a 4 drive raid5 with one missing drive

[Dragan Milivojević]

On Fri, Oct 23, 2015 at 10:46 PM, Marek <mlf.conv@gmail.com> wrote:
> dd from mdX doesn't work i tried it even with testdisk, what you get
> is mixed up data, incomplete files.

As far as dd is concerned /dev/mdX is just another block device so it works
as expected.

Re: Fwd: manually destriping a 4 drive raid5 with one missing drive

[Phil Turmel]

Hi Marek,

On 10/23/2015 04:46 PM, Marek wrote:
> On Fri, Oct 23, 2015 at 7:49 PM, Phil Turmel <philip@turmel.org> wrote:
>> On 10/23/2015 12:20 PM, Marek wrote:
>>> Not sure if it's destrip or destripe but it's basically like puzzle
>>> you take a block from each drive according to the layout you are using
>>> e.g. Left symmetric and then write it down in that order computing
>>> missing blocks from parity blocks - this way you would write an image
>>> which you can mount without using mdadm. Data restoration companies
>>> are using this technique.
>>
>> No special tool required.  Obtain a new drive big enough to hold your
>> entire array and 'dd' from /dev/mdX to your new drive.

> dd from mdX doesn't work i tried it even with testdisk, what you get
> is mixed up data, incomplete files.

Well, that suggests you've done more than just a forced resync.  Pretty
much the only way to get this is to screw up the device order with
"mdadm --create --assume-clean"

You'll need to provide a great deal of data about your array and
precisely what you've done to it.

> { Google mail on iPad doesn't support plain text, who knew :/ }

{Top-posting fixed. Gmail screws this up by default, too.}

Phil