[dm-devel] RHEL6.6 dm-cache and dm-era

[Romu]

2014-09-25 18:19 GMT+08:00 Heinz Mauelshagen <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
>  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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