Re: [PATCH] disk/mdraid1x: Fix >2TB RAID detection with BIOS

[Andrei Borzenkov]

18.11.2016 19:49, Robert LeBlanc пишет:
> Based on debug info, GRUB is requesting to read the end of the drive
> to read the mdadm 1.0 superblock and gets the following message:
> 
> kern/disk.c:421: Read out of range: sector 0x27fffffc8 (attempt to
> read or write outside of disk 'hd0').
> 

Is MD RAID on whole disk or partition? What partition label - MBR or
GPT? Could you post fdisk -l from Linux (if your fdisk does not support
GPT, use "gdisk -l /dev/sdX")?

> My understanding is that BIOS can only access 2TB of disk so this
> makes sense. This patch turns this error from fatal in detecting mdadm
> RAID arrays into a non-critical error so that other versions of
> metadata can still be checked. Where I was running into the problem
> was that we have a 5TB disk with mdadm metadata version 1.2 and we
> could not get the md/0 to show up in GRUB because after the error, it
> never tried to check the other mdadm metadata versions. Once this
> patch was in place, the md/0 showed up and we were able to boot the
> box because /boot on the mdadm RAID was below the 2TB BIOS limit.
> 
> mdadm metadata 1.0 superblock is located 8-12KB from the end of the disk
> mdadm metadata 1.1 superblock is located at sector 0 of the disk/partition
> mdadm metadata 1.2 superblock is located at sector 8 of the disk/partition
> 
> The loop was
> for i=0; i<3; i++{
>   check for the metadata
>   if error {
>     return NULL
>   }
>   return superblock info
> }
> 
> So if an error occurs when checking one type of metadata, it does not
> try the other types to see if they exist. This patch fixes that.
> 
> I hope that clears things up, let me know if you have additional questions.
> ----------------
> Robert LeBlanc
> PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1
> 
> 
> On Thu, Nov 17, 2016 at 9:16 PM, Andrei Borzenkov <address@hidden> wrote:
>> 17.11.2016 23:09, Robert LeBlanc пишет:
>>> When a mdadm RAID array is on a drive larger than 2TB, the array is not
>>> able to be detected and as such even if the array has a partition that
>>> holds /boot under the 2TB limit, it is unable to boot the machine. This
>>> is caused by metadata 1.0 being tested first which allocates the
>>> superblock at the end of the device. When it tries to access the end of
>>> the device it throws an error and the code returns without trying to
>>
>> Why read returns error here and how it is related to device size?
>>
>>> find the superblock at other locations (metadata 1.1 and 1.2). This
>>> patch changes the error to not be fatal and allow for the checking for
>>> the other metadata versions and allowing the machine to boot as long as
>>> /boot is under the 2TB BIOS limit. This won't cause issues with 1.0
>>> metadata because GRUB is able to read the partitions from the front of
>>> the drive/partition without having to determine the data offset, since
>>> the data for metadata 1.0 starts at sector 0.
>>>
>>> Signed-off-by: Robert LeBlanc <address@hidden>
>>> ---
>>>  grub-core/disk/mdraid1x_linux.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/grub-core/disk/mdraid1x_linux.c 
>>> b/grub-core/disk/mdraid1x_linux.c
>>> index 7cc80d3..cc7350c 100644
>>> --- a/grub-core/disk/mdraid1x_linux.c
>>> +++ b/grub-core/disk/mdraid1x_linux.c
>>> @@ -148,7 +148,7 @@ grub_mdraid_detect (grub_disk_t disk,
>>>
>>>        if (grub_disk_read (disk, sector, 0, sizeof (struct 
>>> grub_raid_super_1x),
>>>                         &sb))
>>> -     return NULL;
>>> +     continue;
>>>
>>>        if (sb.magic != grub_cpu_to_le32_compile_time (SB_MAGIC)
>>>         || grub_le_to_cpu64 (sb.super_offset) != sector)
>>>
>>