Check status of background destroy

[Xin LI]

Try setting vfs.zfs.free_max_blocks to 100000 (this is an arbitrary number,
can be larger, limits maximum blocks being freed per txg; see
https://svnweb.freebsd.org/base?view=revision&revision=271532 for details).

You can inspect the progress with DTrace by looking at zfs-dbgmsg.

On Wed, Jan 4, 2017 at 10:30 AM, Freddie Cash <fjwcash at gmail.com> wrote:

> Is there a way to check the progress of a background destroy process?
>
> I did a very bad thing in the middle of December.  "zfs destroy -r
> poolname/dataset", where there's approx 40 TB of data in that dataset,
> spread across about 400 snapshots, sitting on a dedupe-enabled pool.  :(
>  (Usually, I delete individual snapshots, but thought I would try a
> recursive destroy instead.)
>
> Needless to say, the 128 GB of RAM in the box, with 128 GB of L2ARC on SSD,
> is not enough to hold the DDT, and the box deadlocks after about 8 hours of
> disk churning.  Once Wired memory goes above 120 GB, the system is
> unresponsive to everything, including pings.
>
> During that 8 hour period, the pool is usable; I can read and write data to
> the pool, I can create and destroy snapshots, and I can receive snapshots
> from other systems.  But the background destroy continues to run after
> every boot, continues to churn through RAM, and locks everything up after
> about 8 hours.
>
> This has been going on for several weeks now.
>
> Is there any way to check the progress of the background destroy to see how
> much longer this will continue, how much data has been freed, how much of
> the DDT has been updated, etc?  "zfs list" shows very little change in free
> space.
>
> Or am I just going to have to live with resetting the box every 8-10 hours
> for the next few weeks?  Unfortunately, adding more RAM to the box isn't an
> option right now.  :(
>
> --
> Freddie Cash
> fjwcash at gmail.com
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