Hi Song
Thanks so much for you kindly response.
On 4/10/19 1:40 AM, Song Liu wrote:
> On Tue, Apr 9, 2019 at 2:55 AM jianchao.wang <jianchao.w.wang@xxxxxxxxxx> wrote:
>>
>> Hi all
>>
>> In analyse_stripe
>>
>> is_bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
>> &first_bad, &bad_sectors);
>>
>> clear_bit(R5_Insync, &dev->flags);
>> if (!rdev)
>> /* Not in-sync */;
>> else if (is_bad) {
>> /* also not in-sync */
>> if (!test_bit(WriteErrorSeen, &rdev->flags) &&
>> test_bit(R5_UPTODATE, &dev->flags)) {
>> /* treat as in-sync, but with a read error
>> * which we can now try to correct
>> */
>> set_bit(R5_Insync, &dev->flags);
>> set_bit(R5_ReadError, &dev->flags);
>> }
>> }
>> If there is any bad block in the range of a read, it will fall from cache-bypass
>> to stripe-cache. With the R5_UPTODATE checking here, we may try to read from this
>> badblock instead of attempting to calculate the data directly.
>>
>> Why do we need the R5_UPTODATE here ?
>>
>> From the comment of the commit,
>> "
>> We can only treat a known-bad-block like a read-error if
>> we have the data that belongs in that block
>> "
>
> When there is read error, we would like to write the data again, so the drive
> can remap the broken sector. This is only possible when we have the data
> up to date (calculated from other data block and parity). If the data is not up
> to date, we will need to initiate repair (read other blocks for the stripe, and
> recover the data). Once this block is up to date, we will go ahead fix the
> read error on the next iteration.
If we don't set R5_ReadError here, how to trigger the repair to recalculate the data from
other data and parity in the stripe ?
Try to read the badblock and set this R5_ReadError after read failure in raid5_end_read_request ?
It seems meaningless.
Is this should be that trigger a repair directly if the block is known bad block ?
In commit 31c176ecdf3563140e6395249eda51a18130d9f6, say we should avoid read from known badblocks.
Thanks
Jianchao
>
> Does this make sense?
>
> Thanks,
> Song
>
>
>>
>> Would anyone please help to clarify the reason ?
>>
>> Thanks in advance
>> Jianchao
>>
>
