The future of HAMMER1

Xin LI delphij at
Fri Jul 20 14:12:00 PDT 2018

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.

> 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

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