Re: RHEL6.6 dm-cache and dm-era

[Heinz Mauelshagen <heinzm@redhat.com>]

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Romu,

did you initialize the metadata device before trying to create the era 
target?
Zeroes in the first KBs will do.

Yes, check for NULL in era_destroy is needed to  handle the error path 
you hit properly.

Heinz

On 09/26/2014 05:16 AM, Romu Hu wrote:
> On 2014/9/25 22:57, Heinz Mauelshagen wrote:
>> Romu,
>>
>> "dmsetup create MyEra --table "0 20971520 /dev/mapper/mpathbp1 
>> /dev/mapper/mpathap1 8"
>>
>> should read
>>
>> dmsetup create MyEra --table "0 20971520 era /dev/mapper/mpathbp1 
>> /dev/mapper/mpathap1 8"
>
> Sorry my bad.
>
> I ran 'dmsetup create MyEra --table "0 20971520 era 
> /dev/mapper/mpathbp1 /dev/mapper/mpathap1 8"' but kernel 
> (2.6.32-494.el6.i686) oopsed:
>
> Sep 25 18:34:11 localhost kernel: device-mapper: era: sb_check failed: 
> magic 0: wanted 2126579579
> Sep 25 18:34:11 localhost kernel: device-mapper: block manager: 
> superblock validator check failed for block 0
> Sep 25 18:34:11 localhost kernel: device-mapper: era: couldn't 
> read_lock superblock
> Sep 25 18:34:11 localhost kernel: BUG: unable to handle kernel NULL 
> pointer dereference at 00000008
> Sep 25 18:34:11 localhost kernel: IP: [<f7e2b3c7>] 
> era_destroy+0x7/0x60 [dm_era]Sep 25 18:34:11 localhost kernel: *pdpt = 
> 0000000032457001 *pde = 00000003fb5fa067
> Sep 25 18:34:11 localhost kernel: Oops: 0000 [#1] SMP
> Sep 25 18:34:11 localhost kernel: last sysfs file: 
> /sys/module/dm_persistent_data/initstate
>
> Perhaps this should be cherry-picked?
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=989f26f5ad308f40a95f280bf9cd75e558d4f18d
>
> The log says sb_check failed, anything wrong with the dmsetup command 
> parameters?
>
> Thanks
> Romu
>
>> On 09/25/2014 04:02 PM, Romu wrote:
>>> 2014-09-25 18:19 GMT+08:00 Heinz Mauelshagen <heinzm@redhat.com 
>>> <mailto:heinzm@redhat.com>>:
>>>
>>>     On 09/25/2014 08:10 AM, Romu Hu wrote:
>>>>     On 2014/9/24 12:10, Brassow Jonathan wrote:
>>>>>     On Sep 22, 2014, at 7:35 AM, Romu wrote:
>>>>>
>>>>>>     I tried the following command to set up my era target but the
>>>>>>     command immediately panics the system and the system reboots.
>>>>>>
>>>>>>     # dmsetup create MyEra --table "0 41941903 era
>>>>>>     /dev/mapper/VG-CacheDataLV_cmeta /dev/mapper/VG-OriginLV 4096"
>>>>>>
>>>>>>     The metadata dev and the origin dev are all part of a LVM
>>>>>>     cache LV. VG-CacheDataLV_cmeta is the cache metadata LV on
>>>>>>     the smaller and faster device, VG-OriginLV is the origin LV
>>>>>>     on the faster and slower device, 41941903 is the total sector
>>>>>>     number of the device of OriginLV (the LV takes 100% space of
>>>>>>     the device), 4096 is the block size of OriginLV, I have run
>>>>>>     'mkfs.ext4 /dev/mapper/VG-OriginLV' before running the
>>>>>>     dmsetup command.
>>>>>>
>>>>>>     Below is the message in /var/log/messages after running the
>>>>>>     dmsetup comnmand:
>>>>>>
>>>>>>     kernel: device-mapper: era: sb_check failed: magic 1623043:
>>>>>>     wanted 2126579579 <tel:2126579579>
>>>>>>     kernel: device-mapper: block manager: superblock validator
>>>>>>     check failed for block 0
>>>>>>     kernel: device-mapper: era: couldn't read_lock superblock
>>>>>>
>>>>>>
>>>>>>     Any idea?
>>>>>>
>>>>>
>>>>>     Sorry, I haven't used dm-era yet. However, it does appear that
>>>>>     you are perhaps specifying the wrong devices when creating the
>>>>>     era device?  Looks like you might be allowing the era target
>>>>>     and the cache target to use the same metadata area at the same
>>>>>     time - causing them to corrupt each other's metadata area?
>>>>>
>>>>>      brassow
>>>>
>>>>     I think the dmsetup command to set up an era target should be
>>>>     something like this:
>>>>
>>>>     # dmsetup create MyEra --table "0 sector_number era
>>>>     metadeta_dev origin_dev block_size"
>>>>
>>>>     My questions:
>>>>
>>>>     1) How to calculate sector_number?  According to
>>>>     https://www.kernel.org/doc/Documentation/device-mapper/era.txt,
>>>>     I guess it should be (4 * nr_blocks) bytes + buffers, but what
>>>>     is nr_blocks and what is buffers?
>>>
>>>     No calculation: it's the size of your era target in sectors.
>>>     Typically "blockdev --getsz origin_dev"
>>>
>>>>     2) Any documentation for dmsetup tables?
>>>
>>>     Look for examples in the kernel source trees
>>>     Documentaion/device.mapper.
>>>
>>>     table line syntax is: "start_sector length_in_sectors <target>
>>>     <target_arguments{0,N}>"
>>>
>>>>     3) Both my metadata_dev and origin_dev are 10G partitions, is
>>>>     this all right?
>>>
>>>     Metadata device size is plenty but that depends on how many eras
>>>     with how many updates you want to have.
>>>
>>>>     4) My origin_dev is a ext4 filesystem with a block size of
>>>>     4096, so the block_size in the command line should also be 4096?
>>>
>>>     You may use 4096 = _8_ sectors, you used 4096 sectors = 2MB below.
>>>     It's the granularity the era target housekeeps blocks for.
>>>
>>>>
>>>>     I tried the following command:
>>>>
>>>>     # dmsetup create MyEra --table "0 160000 era
>>>>     /dev/mapper/mpathap1 /dev/mapper/mpathbp1 4096"
>>>
>>>     May not be  same physical device for data and metadata!
>>>     If it is, thta'd explain your oops.
>>>
>>>     # dmsetup create MyEra --table "0 $(blockdev --getsz
>>>     /dev/mapper/mpathbp) era whatever_disctinct_metadata_device
>>>     /dev/mapper/mpathbp1 8"
>>>
>>>     Would use 8 sector block size (which is tiny!) with disctinct
>>>     metadata and data devices (presumabyl your ext4 sits on
>>>     /dev/mapper/mpathbp1)
>>>
>>>     Heinz
>>>
>>>
>>> Heinz, thank you for your help!
>>>
>>> My origin dev is 10G so total sector number is 20971520. 
>>>  /dev/mapper/mpathbp1 (/dev/dm-6) is the metadata dev, 
>>> /dev/mapper/mpathap1 (/dev/dm-7) is the origin dev, they are on 
>>> different LUNs.
>>>
>>> I tried the following commands:
>>>
>>> # dmsetup create MyEra --table "0 20971520 /dev/mapper/mpathbp1 
>>> /dev/mapper/mpathap1 8"
>>> # Target type name /dev/mapper/mpathbp1 is too long.
>>> # Command failed
>>>
>>> # dmsetup create MyEra --table "0 20971520 /dev/dm-6 /dev/dm-7 8"
>>> # device-mapper: reload ioctl on MyEra failed: Invalid argument
>>> # Command failed
>>>
>>> And when executing the second command I see the following in 
>>> /var/log/messages:
>>>
>>> Sep 25 06:37:48 localhost kernel: device-mapper: table: 253:8: 
>>> /dev/dm-6: unknown target type
>>> Sep 25 06:37:48 localhost kernel: device-mapper: ioctl: error adding 
>>> target to table
>>> Sep 25 06:37:48 localhost multipathd: dm-8: remove map (uevent)
>>> Sep 25 06:37:48 localhost multipathd: dm-8: devmap not registered, 
>>> can't remove
>>> Sep 25 06:37:48 localhost multipathd: dm-8: remove map (uevent)
>>> Sep 25 06:37:48 localhost multipathd: dm-8: devmap not registered, 
>>> can't remove
>>>
>>> Then I run 'mkfs.ext4 /dev/dm-6' and tried the second command again 
>>> but got the same result.
>>>
>>> Any idea?
>>>
>>> Thanks
>>> Romu
>>>
>>>
>>> --
>>> dm-devel mailing list
>>> dm-devel@redhat.com
>>> https://www.redhat.com/mailman/listinfo/dm-devel
>>
>>
>>
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>
>
>
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-- 
===============================================================
Heinz Mauelshagen                               +49 2626 141200
Consulting Development Engineer             FAX +49 2626 924446
Red Hat GmbH
Am Sonnenhang 11
56242 Marienrachdorf
Germany                                       heinzm@redhat.com
===============================================================


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