* Re: [linux-lvm] [dm-devel] dm-thin metadata: can two device_id's have the same transaction_id ?
[not found] <alpine.LRH.2.11.1603112308440.30893@mail.ewheeler.net>
@ 2016-03-12 8:44 ` Zdenek Kabelac
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From: Zdenek Kabelac @ 2016-03-12 8:44 UTC (permalink / raw)
To: Eric Wheeler, dm-devel, LVM general discussion and development
Dne 12.3.2016 v 00:14 Eric Wheeler napsal(a):
>
> 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"
> }
> }
>
Hi
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
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