volume management

[Ivan Voras]

Pawel Jakub Dawidek wrote:

> Ivan, as you probably already find out this is not an easy task and it
> gets more complex when SU comes into play or any async operations,
> because there is noone waiting for the error to return.
> 
> Maybe you for now allow to set two modes of handling ENOSPC
> (configurable by the user):
> 1. Panic if there is no physical storage. This way you protect
>    consistency. You already printed a warning that gvirstor is running
>    out of physical storage, so administrator has a chance to do the job.

I really don't want to do that :(

> 2. Hang until the storage is available. Just don't return from I/O until
>    new provider is attached to gvirstor.

I'd rather do this. I'm still worried about the possibility some 
unexpected softupdates timer will to the wrong thing here, but I'll try it.

> You may want to leave 3rd option to just return ENOSPC, because besides
> UFS there can be other gvirstor consumers that handle errors more
> properly.

Ok.

> You may also want to consider sending warnings to devd, which I do in
> ZFS (see zfs_fm.c and devd.conf) and should do in others GEOM classes.
> This way administrator can configure sending an e-mail when gvristor is
> running out of storage.

Good idea, I'll look it up.

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