Zdenek Kabelac
2016-03-12 08:44:31 UTC
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?
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"
origin = "backup2.ewheeler.net_14-drbd"
}
}
HiFor 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?
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 = 5735origin = "backup2.ewheeler.net_14-drbd"
}
}
It's rather for linux-lvm list.
Transaction_id is 24bit number - and like may be possible to wrap
although it has not been much tested in such corner case.
(I should probably add some tests around this for lvm2...)
Device_id lvm2 does not recycle ATM - so it just always seeks for
largest and picks +1. But it doesn't mean we could not introduce
recyling at some point.
However at this moment we rather try to use unique numbers to simplify
possible recovery steps - it's fairly simpler.
Regards
Zdenek