[nycbug-talk] DragonFly HAMMER filessytem

Isaac Levy ike at lesmuug.org
Wed Oct 17 13:22:54 EDT 2007

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..."

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  

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?!):

> 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


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