dm-thin metadata: can two device_id's have the same transaction_id ?

[Eric Wheeler <dm-devel@xxxxxxxxxxxxxxxxxx>]

Hello all, 

For thin volumes shown in the lvm VG metadata backups in 
/etc/lvm/backup/pool, can any two device_id's have the same 
transaction_id, ever?

Otherwise, can I assume that the device_id and transaction_id are both 
unique, or is only the tuple (transaction_id,device_id) unique?

For example:

my-thin-vol {
        id = "M8fkBP-pFe8-Z6K0-0f7N-HAFM-Mv2v-KOTmM3"
        status = ["READ", "WRITE", "VISIBLE"]
        flags = ["ACTIVATION_SKIP"]
        creation_host = "hv1.ewheeler.net"
        creation_time = 1452374892      # 2016-01-09 13:28:12 -0800
        segment_count = 1

        segment1 {
                start_extent = 0
                extent_count = 3072     # 48 Gigabytes

                type = "thin"
                thin_pool = "data-pool"
>>>>>>>>>>>>    transaction_id = 9843
                device_id = 5735
                origin = "backup2.ewheeler.net_14-drbd"
        }
}


--
Eric Wheeler

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