zpool import hangs when out of space - Was: zfs pool import hangs on [tx->tx_sync_done_cv]

[K. Macy]

On Mon, Oct 13, 2014 at 6:24 PM, Mark Martinec
<Mark.Martinec+freebsd at ijs.si> wrote:
> On 10/14/2014 03:15, K. Macy wrote:
>>
>> What is using the extra space in the pool? Is there an unmounted
>> dataset or snapshot? Do you know how to easily tell? Unlike txg and
>> zio processing I don't have the luxury of having just read that part
>> of the codebase.
>
>
> Most likely the snapshots (regular periodic snapshots).
> Changes after upgrading an OS can maybe take an additional 50%
> of space (just guessing). Btw, ashift=12.
> Still can't see how that would amount to 4 GiB, but it's possible.
>

Disconcerting. Is this something that others are likely to hit? Should
accounting for writes fail with ENOSPC a bit earlier so that we never
reach a state like this? I.e. non-metadata writes will fail at a lower
threshold than data or if that is already the case, reduce the
threshold further.

-K