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

[Romu Hu <huruomu@gmail.com>]

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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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>
>
>
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