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?
2) Any documentation for dmsetup tables?
3) Both my metadata_dev and origin_dev are 10G partitions, is this all right?
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?

I tried the following command:

# dmsetup create MyEra --table "0 160000 era /dev/mapper/mpathap1 /dev/mapper/mpathbp1 4096"

It immediately panics the kernel (2.6.32-494.el6.i686) with the following info in /var/log/messages:

Sep 24 22:44:22 localhost kernel: device-mapper: era: sb_check failed: magic 0: wanted 2126579579Sep 24 22:44:22 localhost kernel: device-mapper: block manager: superblock validator check failed for block 0Sep 24 22:44:22 localhost kernel: device-mapper: era: couldn't read_lock superblockSep 24 22:44:22 localhost kernel: BUG: unable to handle kernel NULL pointer dereference at 00000008Sep 24 22:44:22 localhost kernel: IP: [<f7e9a3c7>] era_destroy+0x7/0x60 [dm_era]Sep 24 22:44:22 localhost kernel: *pdpt = 0000000001945001 *pde = 00000003ff97f067Sep 24 22:44:22 localhost kernel: Oops: 0000 [#1] SMPSep 24 22:44:22 localhost kernel: last sysfs file: /sys/module/dm_mod/initstate

Thanks
Romu