The future of HAMMER1

Jasse Jansson jasse at
Fri Jul 20 15:12:45 PDT 2018

On 2018-07-20 23:12, Xin LI wrote:
> On Fri, Jul 20, 2018 at 2:07 PM Rickard von Essen
> <rickard.von.essen at> wrote:
>> Both "scrub of death" and "you have to use ECC ram when you use ZFS" are myths.
> +1.  ECC is not a requirement for ZFS, and ZFS only rewrites data when
> it sees checksum mismatch AND the replica were correct, so the chance
> of scrub damaging data is extremely low because you need at least two
> flipped bits in the first place.
> You do want to use ECC RAM if the data is valuable though; the small
> price difference will definitely worth it if you ever see a corruption
> that you can't recover from.

In my experience "I" am the biggest threath to my stored pics and other 
stuff I stored in my servers in my basement.
I have accidently countersunk an external HD used for backups twice in 
the last 10 years, and I doubt I'll have ever been so close to a lethal 
heart attac, twice again.
Both times all the files could be restored using a data recovery program 
I can't remember the name of right now.
I don't take that risk anymore.

My main server runs FreeNAS with a 5-disk raidZ volume (ECC RAM), 
scrubbed twice every month.
My backup server also runs FreeNAS with a 5-disk RaidZ volume (ECC RAM), 
also scrubbed twice every month.
Both servers are attached to UPS power.
The backup server rsynch's the whole volume every third night.
I log in regularly to my servers to check they are OK.
I also make sure to replace the HD's every 3 years.

You really think I would risk another near death experience by running 
NON-ECC RAM for the little price difference there is today.
But it's your pics/data/files and your choice.

Oh, btw, if you are going to buils a new server with ECC memory, make 
sure the CPU supports it, the latest i3's don't.

>> One good discussion on the topic can be found on:
>> On Fri, Jul 20, 2018, 22:37 Predrag Punosevac <punosevac72 at> wrote:
>>> Hi,
>>> I was wondering if Matt and the other developers involved can shed some
>>> light onto the future of HAMMER1 and ultimately of DragonFly.
>>> I started dicking with DragonFlyBSD 7-8 years ago mostly due to my
>>> curiosity about HAMMER. I tried few times in the past to use DF as a
>>> main file server at the place of my employment just quickly to reverse
>>> back to ZFS and FreeBSD but my home file server is still happily running
>>> dfly# uname -a
>>> DragonFly 5.2-RELEASE DragonFly v5.2.2-RELEASE #17:
>>> dfly# mount
>>> ROOT on / (hammer, noatime, local)
>>> devfs on /dev (devfs, nosymfollow, local)
>>> /dev/serno/B620550018.s1a on /boot (ufs, local)
>>> /pfs/@@-1:00001 on /var (null, local)
>>> /pfs/@@-1:00002 on /tmp (null, local)
>>> /pfs/@@-1:00003 on /home (null, local)
>>> /pfs/@@-1:00004 on /usr/obj (null, local)
>>> /pfs/@@-1:00005 on /var/crash (null, local)
>>> /pfs/@@-1:00006 on /var/tmp (null, local)
>>> procfs on /proc (procfs, local)
>>> DATA on /data (hammer, read-only, noatime, local)
>>> BACKUP on /backup (hammer, noatime, local)
>>> /dev/serno/5QG00XF0.s1e at DATA on /test-hammer2 (hammer2, local)
>>> /data/pfs/@@-1:00001 on /data/backups (null, local)
>>> /data/pfs/@@-1:00002 on /data/nfs (null, NFS exported, local)
>>> I feel the time to physically rebuild my home file server slowly
>>> approaching so I would like to be ready for that day.
>>> In the light of the fact that HAMMER2 is out and recommended for root
>>> partition does HAMMER have any future? I see Tomohiro Kusumi still
>>> having a commit or two a month which touches HAMMER but it seems that
>>> even his commits are minor bug fixes related to his work/poking with
>>> HAMMER2. Is everyone else done playing with HAMMER1?
>>> Is HAMMER2 now stable enough to guarantee consistency of my data? My
>>> concern is that it typically takes at least 10 years for a file system
>>> to mature under lot of use and abuse by a much wider community than DF.
>>> BTRFS is vaporware even after major investment since 2007. With the size
>>> of the DF community I feel it might takes 20-30 years for HAMMER2 to be
>>> trully safe.
>>> One of the main advantages for me personally of HAMMER1 over ZFS besides
>>> fine grained history was that it seems to be ok-ish with non-ECC RAM.
>>> Scrub of death
>>> is real thing and I feel very uncomfortable using ZFS on my cheap home
>>> hardware. I know that under non-budgetary constrains I should use ECC
>>> memory with DF as well. How safe HAMMER2 is with non-ECC memory?
>>> Cheers,
>>> Predrag

More information about the Users mailing list