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List:       linux-raid
Subject:    Re: mdadm raid1 regression
From:       Vasiliy Tolstov <v.tolstov () selfip ! ru>
Date:       2013-04-22 9:56:07
Message-ID: CACaajQsK9re65LQ85Xy_G7y0h6AcRm6bN0A6q9Qd2P72NBZQbw () mail ! gmail ! com
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Very cool =). But i think with latest patches for mdadm with ability
to control data offset we can use "vanilla" mdadm =).

2013/4/22 Sebastian Riemer <sebastian.riemer@profitbricks.com>:
> On 22.04.2013 08:28, Vasiliy Tolstov wrote:
>>> Why are you doing that?
>>
>> Our storage have two nodes each provides disk via srp to nodes. On
>> each node we create separate lvm (we not using clvm) and assemble md.
>> Sometimes we resize lvm and need to zero superblock, becouse sometimes
>> we can still have old mdadm data on lvm part (from previous user for
>> example). And then we add disk to raid we can get sometimes broken
>> data (invalid sync).
>>
>>>
>>>> P.S. If i use mdadm 3.2.2 i get data offset 4096 that not breaks data,
>>>> but inconsistent with older versions.
>>>
>>> I suggest you use mdadm 3.2.2 then.
>>
>> Yes, i'm already do that, but i think that lates mdadm version with
>> data-offset patches can solve my problems. Is that possible to correct
>> it behaviour and write in docs which data offset used in which version
>> of mdadm?
>>
>>>
>>>> P.P.S. I'm try to specify --data-offset when create array but as i see
>>>> - its ignored and data offset still have 8192).
>>>
>>> I'll try to make sure that works correctly for the next release.
>>> Thanks for the report.
>
> So you use MD RAID-1 on the SRP initiator for replication?
>
> So do we. We've just hacked mdadm to always use one LV extent (4 MiB)
> for the "head room" with RAID-1 and don't allow reshape of RAID-1
> anymore. This makes it very easy to calculate. We had to change mdadm
> and the MD kernel code anyway to provide advanced replication features.
>
> We've even got safe VM live migration with it and raw-to-md migration
> letting the MD syncer do the job to sync the data from the raw device to
> the MD devices. :-)
> Replication of virtual storage doesn't really work without custom
> hacking with MD. This use case is very hard to merge with mainline
> behavior. But the required changes are relatively small.
>
> Cheers,
> Sebastian



-- 
Vasiliy Tolstov,
e-mail: v.tolstov@selfip.ru
jabber: vase@selfip.ru
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