HEADS UP: ZFS v28 merged to 8-STABLE

Jeremy Chadwick freebsd at jdc.parodius.com
Fri Jun 10 21:12:05 UTC 2011

On Mon, Jun 06, 2011 at 12:53:11PM +0200, Martin Matuska wrote:
> I have merged ZFS version 28 to 8-STABLE (revision 222741)

Follow-up, since we're gradually upgrading our ZFS-based RELENG_8
servers to ZFSv28.  Committers/those involved should see my very last

First, server upgrades:

We've upgraded 2 of the 4 (including updating zfs and zpools), and so
far things are working wonderfully.  One of those 2 boxes is our NFS
filer (which also does backups via rsync/rsnapshot), so that one's been
a big worry-point of mine.  The next rsync/rsnapshot runs tonight, so
I'll be awake watching intently.  All these systems are graphed via
bsnmpd (memory, CPU, disk I/O, etc.).

Second, performance tweaks:

We're testing changing to our tweaks; the following directives have been
commented out in our /boot/loader.conf files (e.g. we're now using

# vfs.zfs.prefetch_disable="1"

And the following tunable has been removed completely, because it's
now the default in ZFSv28 (see cvsweb, look at line 40 of the relevant
commit for src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/txg.c):


Finally, talking a bit about dedup:

In the ZFSv28 commit, did the zfs.8 man page get updated? I find no
mention of the dedup property in the zfs(8) man page, and yes I did
remove the old /usr/share/man/cat8/zfs.8.gz file.

We tried using dedup on one of our systems, but within 10-15 minutes
turned it off.  I believe the added CPU overhead of dedup was causing
the system to act "bursty" in other non-ZFS-related tasks; e.g. turn on
dedup, then in a SSH window hold down the letter "q" indefinitely, then
in another window do some ZFS I/O.  The "q" would stall for 1-2 seconds
at times (SSH connectivity was via direct private LAN, so network
latency was not what we seen).  Without dedup this behaviour wasn't seen
at all.  I'm happy to try any advice/patches on a locally-accessible
box (e.g. private LAN, VGA console is right behind me, etc.).

I have not tried tinkering with the following settings to find out
what may relieve this issue.  I'm referring to the sections titled
"Trust or verify" and "Selecting a checksum" on Jeff's blog here:


All in all, thank you everyone for the work that's gone in to MFC'ing
this to RELENG_8.  I really do mean that.  I'm a harsh bastard on the
mailing lists, no question about it.  But I always appreciate people
doing the grunt work that I myself cannot do (over my head).  I state
this seriously: if any of you folks who participated in this MFC have
donation links (PayPal, etc.), please give them to me.  You absolutely
will see some worthwhile kick-backs for your efforts, with no strings
attached.  Just my way of saying "thank you".

| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                   Mountain View, CA, US |
| Making life hard for others since 1977.               PGP 4BD6C0CB |

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