On Sat, Apr 18, 2020 at 6:53 AM Void Star Nill <void.star.nill@xxxxxxxxx> wrote:
>
> Hello,
>
> How frequently do RBD device names get reused? For instance, when I map a
> volume on a client and it gets mapped to /dev/rbd0 and when it is unmapped,
> does a subsequent map reuse this name right away?
Yes.
>
> I ask this question, because in our use case, we try to unmap a volume and
> we are thinking about adding some retries in case unmap fails for any
> reason. But I am concerned about race conditions such as the following:
> 1. thread 1 calls unmap, but the call times out and returns in the process,
> but in the background unmap request does go through and the device gets
> removed
> 2. thread 1 does a retry based on the device name.
>
> If between 1 and 2, another thread tries to map another volume and if it
> gets mapped to same device right after previous unmap was successful, then
> in step 2, we will be trying to unmap a device that doesn't belong to
> previous map.
>
> So I want to know how frequently do the device names get reused, and if
> there is a way to keep them using new names until they round back after a
> max limit.
No, there is no way.
Use image names instead of device names, i.e. "rbd unmap myimage"
instead of "rbd unmap /dev/rbd0".
Thanks,
Ilya
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