Thank you Eugen and Nathan!
uint64 is big enough, no concerns any more.
Tony
________________________________________
From: Nathan Fish <lordcirth@xxxxxxxxx>
Sent: August 4, 2023 04:19 AM
To: Eugen Block
Cc: ceph-users@xxxxxxx
Subject: Re: What's the max of snap ID?
2^64 byte in peta byte
= 18446.744073709551616 (peta⋅byte)
Assuming that a snapshot requires storing any data at all, which it
must, nobody has a Ceph cluster that could store that much snapshot
metadata even for empty snapshots.
On Fri, Aug 4, 2023 at 7:05 AM Eugen Block <eblock@xxxxxx> wrote:
>
> I'm no programmer but if I understand [1] correctly it's an unsigned
> long long:
>
> > int ImageCtx::snap_set(uint64_t in_snap_id) {
>
> which means the max snap_id should be this:
>
> 2^64 = 18446744073709551616
>
> Not sure if you can get your cluster to reach that limit, but I also
> don't know what would happen if you actually would reach it. I also
> might be misunderstanding so maybe someone with more knowledge can
> confirm oder correct me.
>
> [1] https://github.com/ceph/ceph/blob/main/src/librbd/ImageCtx.cc#L328
>
> Zitat von Tony Liu <tonyliu0592@xxxxxxxxxxx>:
>
> > Hi,
> >
> > There is a snap ID for each snapshot. How is this ID allocated, sequentially?
> > Did some tests, it seems this ID is per pool, starting from 4 and
> > always going up.
> > Is that correct?
> > What's the max of this ID?
> > What's going to happen when ID reaches the max, going back to start
> > from 4 again?
> >
> >
> > Thanks!
> > Tony
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>
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