[dm-devel] RHEL6.6 dm-cache and dm-era
Heinz Mauelshagen
heinzm at redhat.com
Mon Sep 29 10:12:59 UTC 2014
On 09/29/2014 04:31 AM, Romu Hu wrote:
> 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?
It is the proper way to address it when using dmsetup.
MInd you dmsetup is a low-level tool which is very handy for
testing/evatuation
like in your use case.
Ultimately dm-era will be supported by lvm and eventually other higher
level tools,
which will be in charge of doing metadata device initialization.
Heinz
>
> 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 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
>> Germanyheinzm at redhat.com
>> ===============================================================
>>
>>
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>
>
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