[BUGS] NFS root and GJournal

[Peter Jeremy]

On 2015-Sep-23 03:39:21 +0200, Peter Ross <Peter.Ross at bogen.in-berlin.de> wrote:
>I am playing around with virtualisation and ZFS etc and have some  
>thoughts related to booting from a small device (having a SSD e.g.)  
>and using a storage server having ZFS and all that "fun staff" (BTW: I  
>have done jail deployments for 4 years and simply loved it, it is what  
>Dockers should be;-)
>
>I wonder whether it is possible to run GJournal in front of it, as  
>described in the handbook for UFS.

It's possible to run gjournal in front of anything but it won't help ZFS
and will probably reduce its resilience.  Firstly, ZFS is a CoW filesystem
so it doesn't generate as much random write load.  Secondly, ZFS has its
own journal (the ZIL).  Finally, ZFS keeps four sets of uberblocks in each
vdev and is very careful to update these in such a way as to minimise the
impact of a crash or power outage.  Having a gjournal in front of a ZFS
vdev would mean that uberblock updates are virtually guaranteed to be
merged into a the same area on the gjournal device - where they are
likely to be all lost.

-- 
Peter Jeremy
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