Re: MTD RAID

[Dongsheng Yang <dongsheng.yang@easystack.cn>]

On 08/19/2016 02:49 PM, Boris Brezillon wrote:
> Hi Dongsheng,
>
> On Fri, 19 Aug 2016 14:34:54 +0800
> Dongsheng Yang <dongsheng081251@gmail.com> wrote:
>
>> Hi guys,
>>      This is a email about MTD RAID.
>>
>> *Code:*
>>      kernel:
>> https://github.com/yangdongsheng/linux/tree/mtd_raid_v2-for-4.7
> Just had a quick look at the code, and I see at least one major problem
> in your RAID-1 implementation: you're ignoring the fact that NAND blocks
> can be or become bad. What's the plan for that?

Hi Boris,
     Thanx for your quick reply.

     When you are using RAID-1, it would erase the all mirrored blockes 
when you are erasing.
if there is a bad block in them, mtd_raid_erase will return an error and 
the userspace tool
or ubi will mark this block as bad, that means, the 
mtd_raid_block_markbad() will mark the all
  mirrored blocks as bad, although some of it are good.

In addition, when you have data in flash with RAID-1, if one block 
become bad. For example,
when the mtd0 and mtd1 are used to build a RAID-1 device mtd2. When you 
are using mtd2
and you found there is a block become bad. Don't worry about data 
losing, the data is still
saved in the good one mirror. you can replace the bad one device with 
another new mtd device.

My plan about this feature is all on the userspace tool.
(1). mtd_raid scan mtd2 <---- this will show the status of RAID device 
and each member of it.
(2). mtd_raid replace mtd2 --old mtd1 --new mtd3.   <---- this will 
replace the bad one mtd1 with mtd3.

What about this idea?

Yang
>
> Regards,
>
> Boris
>
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