[nycbug-talk] DragonFly HAMMER filessytem

Charles Sprickman spork at bway.net
Wed Oct 17 16:43:27 EDT 2007

On Wed, 17 Oct 2007, Isaac Levy wrote:

> Hi All,
> On Oct 15, 2007, at 12:18 PM, Pete Wright wrote:
>> On Mon, Oct 15, 2007 at 11:44:45AM -0400, Yarema wrote:
>>> Ike,
>>> I've gathered you like the ZFS implementation in FreeBSD.
>>> Check out Matt Dillon's HAMMER filesystem design document:
>>> http://Leaf.DragonFlyBSD.org/mailarchive/kernel/2007-10/msg00006.html
>>> ... and why he why he chose not to use Sun's ZFS:
>>> http://Leaf.DragonFlyBSD.org/mailarchive/kernel/2007-10/msg00008.html
> Excellent docs, thanks Yarema for boiling this down to URL's with the
> simplest explanations!
>>> Anyway the December release of DragonFly 2.0 should have a usable
>>> fs.  Should be fun having two kick ass filesystems coming out in
>>> BSDs next
>>> year.
> Agreed :)
> And to be honest, UFS2 isn't all that bad ;)
> Aside from grief as we all begin fsck'ing multi-TB volumes, it's a
> solid performer- and still *the* benchmark classic UNIX filesystem.
> We're lucky in *BSD-land.
>> yea this is really exciting!  i think matt hit's the nail on the head
>> here (wow that's a bad pun) having hammer focus on his clustering
>> goals.
> I see what Hammer is trying to accomplish, and the clustering/
> replication goals are AMAZING- however, I have one big show-stoppers
> for me using it:
> "...A volume is thus limited to 16TB..."

It does look like Matt is planning for the future though, his announcement 
includes this:

   HAMMER's storage management limits it to 32768 volumes, 32768 clusters
   per volume, and 32768 16K filesystem buffers per cluster.   A volume
   is thus limited to 16TB and a HAMMER filesystem as a whole is limited
   to 524288TB.  HAMMER's on-disk structures are designed to allow future
   expansion through expansion of these limits.  In particular, the volume
   id is intended to be expanded to a full 32 bits in the future and using
   a larger buffer size will also greatly increase the cluster and volume
   size limitations by increasing the number of elements the buffer-
   restricted radix trees can manage."

So two things:  only the components are limited to 16TB, a filesystem can 
total 524288TB, and the "on-disk structures" are setup such that the 16TB 
limit can be raised later without redesigning the whole thing.

Dragonfly should be quite the interesting OS in the next few years - it 
sounds like clustering is his goal...


> I can't move foreword with this.  Right now the largest filesystems I
> touch are just over 10TB, so I'm under the limit- but the people
> using them are outgrowing them at a quick pace.  In another year I
> expect to be working with 30TB for single fileservers.
> (btw those boxes use UFS2 on FreeBSD-6-REL, and the boxes are SOOOO
> stable)
> I don't mean to sound macho about the disk space, but it's a real and
> growing concern for me right now.
> Managing it (with new features) is one thing, Hammer and ZFS both
> provide great tools for dealing with the increased space- but the raw
> idea of simply storing more bits is most important.
> --
> Maximum filesystem size comparison (what about maximum file size for
> Hammer btw?):
> Hammer: 16TB
> UFS2: 1YiB (1 Yobibyte =  ) http://en.wikipedia.org/wiki/Yobibyte
> ZFS: 16EiB (Exbibytes) http://en.wikipedia.org/wiki/EiB
> No time to do the math and figure out how many TB fit into a Yobibyte
> or an Exbibyte, but as far as my little brain can comprehend, both
> UFS2 and ZFS will meet my needs in the coming years.
> Sidenote, pretty neat specs (someone should add an entry for Hammer?!):
> http://en.wikipedia.org/wiki/Comparison_of_file_systems
>> I see ZFS as being a great candidate for SAN/NAS solutions - with alot
>> of nice features for jail's etc.
> YES.  ZFS + Jail is SOOOOOO exciting to me!
>> hammer seems to be addressing another very important niche - a well
>> written clustered filesystem.  execellent!
> Sure, yes- but can't it scale beyond 16TB?!  Please?!?!
>> thanks for the heads up!
>> -p
> Rocket-
> .ike
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