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

[Romu Hu <huruomu@gmail.com>]

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On 2014/9/26 18:33, Heinz Mauelshagen wrote:
>
> Romu,
>
> did you initialize the metadata device before trying to create the era 
> target?
> Zeroes in the first KBs will do.

Thanks Heinz, it solved the problem.  Is it the proper way to initialize 
the metadata device of an era target or just a workaround?

Thanks
Romu

> 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
>>>>
>>>>
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>>>> 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
> Germanyheinzm@redhat.com
> ===============================================================
>
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