kern/154930: [zfs] cannot delete/unlink file from full volume -> ENOSPC

[Martin Matuska]

Some more information on this:

Here is a OpenSolaris forums entry:
http://opensolaris.org/jive/thread.jspa?threadID=62037

This is described in Illumos issues as well:
https://www.illumos.org/issues/412

This is quite a serious problem of the ZFS implementation - to delete a
file or a snapshot, you may need free space!

I am quoting Garett D'Amore:
"The problem is that with copy-on-write, when you delete a file you must
create a new copy of the meta data which means a new tree, ultimately.
Its not possible to avoid this, but it is possible that we should
ultimately be able to have a reserve, and only allow operations which
will ultimately remove data once the pool is reduced to nothing more
than this reserve."

Before we have a "reserve" implementation, the only workaround I found
is creating an empty dataset with some reserved space (which you can
free in a case of emergency), e.g.:
zfs create -o mountpoint=none -o reservation=10M tank/reserve

Dňa 22.02.2011 16:50, Matthias Andree  wrote / napísal(a):
> The following reply was made to PR kern/154930; it has been noted by GNATS.
> 
> From: Matthias Andree <mandree at FreeBSD.org>
> To: Martin Matuska <mm at FreeBSD.org>
> Cc: bug-followup at FreeBSD.org
> Subject: Re: kern/154930: [zfs] cannot delete/unlink file from full volume
>  -&gt; ENOSPC
> Date: Tue, 22 Feb 2011 16:06:47 +0100
> 
>  Am 22.02.2011 15:30, schrieb Martin Matuska:
>  > I was unable to reproduce your problem.
>  >
>  > But I was able to reproduce a different situation:
>  > - on a dataset with one or more snapshots I am unable to delete files
>  > (ENOSPC) if the dataset got full.
>  >
>  > If this is your case, then:
>  > - deleting files does not unlink them from the snapshot.
>  > - you must first delete a specific snapshot (or all snapshots linking
>  > the file) to free space.
>  
>  Hi Martin,
>  
>  no snapshots were ever used on the zpools or zfs volumes -- I had 
>  checked that previously. Only truncation of a 20 M file would allow me 
>  to delete files.
>  
>  Best regards
>  Matthias
>  
>  -- 
>  Matthias Andree
>  ports committer
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-- 
Martin Matuska
FreeBSD committer
http://blog.vx.sk