ZFS on top of GELI

[Gerrit Kühn]

On Mon, 11 Jan 2010 15:29:54 -0800 "K. Macy" <kmacy at freebsd.org> wrote
about Re: ZFS on top of GELI:

KM> > That is true, but using a single device for a dedicated ZIL is a huge
KM> > no-no, considering it's an intent log, it's used to reconstruct the
KM> > pool in case of a power failure for example, should such an event
KM> > occur at the same time as a ZIL provider dies, you lose the entire
KM> > pool because there is no way to recover it, so if ZIL gets put
KM> > "elsewhere", that elsewhere really should be a mirror and sadly I
KM> > don't see myself affording to use 2 SSDs for my setup :)

KM> This is  false. The ZIL is used for journalling synchronous writes. If
KM> your ZIL is lost you will lose the data that was written to the ZIL,
KM> but not yet written to the file system proper. Barring disk
KM> corruption, the file system is always consistent.

So how would ZFS behave if ZIL is sitting on a single disk that is then
lost? Throw away the intented writes and continue happily from there on? I
still have some broken volume sitting around that panics the kernel when
trying to replay the (obviously somehow corrupted) ZIL (see
<http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/140433>) and I wonder if
situations like this could be handled by taking out the ZIL drive (only
if there is a dedicated one, of course).


cu
  Gerrit