[dm-devel] RHEL6.6 dm-cache and dm-era
Heinz Mauelshagen
heinzm at redhat.com
Fri Sep 26 10:33:58 UTC 2014
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 at redhat.com
>>> <mailto:heinzm at 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 at 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 at redhat.com
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