[mdlug] [WLUG] building a nas device

[Dan Pritts]

zfs is a filesystem, volume manager, and software raid all rolled
together.  it does full checksums on all data.  

it uses variable stripe width on its RAID5/6 variant, RAIDz/z2, so
it can avoid the RAID5 write hole and slow read-modify-write cycle
(notably, though, this comes at the expense of random read performance).

if you have super-important data or just a single disk, it can write
multiple copies.

snapshots are built in.

administration is a breeze.  

it can trivially make use of a fast device (ssd) as a read cache (L2ARC)
or write cache (ZIL).

it is awesome, although not without its warts.  

On Tue, Jun 01, 2010 at 03:24:46PM -0400, Ethan Allen wrote:
> Not to take this too far off topic but what makes ZFS an advantage of XFS? I
> have never used ZFS but since it was brought up here I thought I would ask.
> 
> On Tue, Jun 1, 2010 at 3:15 PM, Dan Pritts <danno at umich.edu> wrote:
> 
> > On Mon, May 31, 2010 at 12:46:25PM -0400, Joe Landman wrote:
> > > >Do not use RAID5 if you care about ALL of your data; you need double
> > > >redundancy (RAID6) with modern drives.  Why?  You will eventually
> > > >lose a drive.  During rebuild you are reasonably likely to have a
> > > >read error somewhere on another drive.  You may get lucky and this
> > > >is on free space, or it's data you decide you can live without
> > > >(e.g., if i lose one photo out of the 5000 i've taken, no big deal,
> > > >but if i lose them all i'd be sad).
> > >
> > > RAID6 or RAID10.
> >
> > with raid10 you still have a pretty good chance of data loss.
> >
> > http://blog.richardelling.com/2010/02/zfs-data-protection-comparison.html
> >
> > This is pretty much out of the realm of what the OP was looking for
> > though.
> >
> > > ZFS's future outside of commercial paid Solaris licenses is very much in
> > > doubt.
> >
> > one answer to this concern is that the existing code can't be taken
> > back; a freebsd system you build today will work just as well tomorrow.
> >
> > another is that it's possible oracle will give away zfs to gpl;
> > they are funding linux's btrfs.
> >
> > all that said it is certainly possible that future enhancements to
> > zfs will be proprietary.
> >
> > basically for carl's a single NAS this is not an issue.  i would
> > certainly be concerned before designing products around this though
> > :)
> >
> > danno
> > --
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danno
--
dan pritts
danno at umich.edu
734-929-9770