what happens to pool if ZIL dies on ZFS v14

[David Brodbeck]

On Wed, Sep 22, 2010 at 6:00 AM, Martin Simmons <martin at lispworks.com> wrote:
>>>>>> On Tue, 21 Sep 2010 15:38:22 -0700, David Brodbeck said:
>>
>> If you don't have a separate log device, synchronous writes are very
>> slow with the ZIL enabled.  This isn't such a big deal unless you're
>> using NFS, where essentially every write is synchronous.
>
> Is that true for all versions of NFS?  In my experience (on 8.0-RELEASE),
> NFSv2 is indeed synchronous, but NFSv3 does asynchronous flushing (for a
> variety of different client OSes).

It does allow clients to request asynchronous flushing.  My statement
that "essentially every write is synchronous" was a bit of an
overstatement; the problem comes when the client issues a COMMIT,
which happens frequently when doing some operations, such as
extracting tar files.  These are the operations that can get quite
slow when using NFS with the ZIL enabled and no separate log device.
By "quite slow," I mean several minutes to extract a tar file that
takes less than a minute with the ZIL disabled.