Re: I/O errors without erros from underlying device

[NeilBrown <nfbrown@novell.com>]

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On Tue, Dec 08 2015, Arkadiusz Miskiewicz wrote:

> On Monday 07 of December 2015, Arkadiusz Miskiewicz wrote:
>
>> Anyway I would expect my problem to be related to badblock lists which
>> numbers are close to dmesg error message: [  848.988518] Buffer I/O error
>> on dev md7, logical block 3907148544, async page read
>> 
>> > >> http://sprunge.us/XSWI
>> 
>> But how to repair these if write() also fails and
>> http://www.spinics.net/lists/raid/msg49325.html suggests that write should
>> "fix" these (by using replacement blocks I guess) ?
>
> Tried to get rid of badblock lists (well, corruption in that area is better 
> than no access at all):
>
> mdadm --assemble /dev/md7 --force --update=no-bbl
> mdadm: Cannot remove active bbl from /dev/sdae1
> mdadm: Cannot remove active bbl from /dev/sdag1
> mdadm: Cannot remove active bbl from /dev/sdai1
> mdadm: Cannot remove active bbl from /dev/sdn1
> mdadm: Cannot remove active bbl from /dev/sdg
> mdadm: Cannot remove active bbl from /dev/sdad1
> mdadm: /dev/md7 has been started with 10 drives.
>
> Is there a way to archieve that anyway?
>

You probably have bad blocks in multiple disks in the one stripe
(look in /sys/block/md7/md/dev-*/badblocks or something like that to
see).

To get rid of these you would need to write to every block in the
stripe.  I guess I should try to find a way to make that easier.

If you like you could hack mdadm to allow you to remove the bbl even
though they aren't empty.
In super1.c look for:
	} else if (strcmp(update, "no-bbl") == 0) {
		if (sb->feature_map & __cpu_to_le32(MD_FEATURE_BAD_BLOCKS))
			pr_err("Cannot remove active bbl from %s\n",devname);
		else {
			sb->bblog_size = 0;
			sb->bblog_shift = 0;
			sb->bblog_offset = 0;
		}

and change it to be unconditional and also to clear
MD_FEATURE_BAD_BLOCKS.

No warranty expressed or implied.

NeilBrown

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