

Z-410: How ZFS is slowly making its way to Mac OS X - thehigherlife
http://arstechnica.com/apple/news/2011/03/how-zfs-is-slowly-making-its-way-to-mac-os-x.ars

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Derbasti
This. I want this!

Hard disks are the only part of a computer that is not replaceable. Everything
that improves data integrity is improving computer usage as a whole. Improving
data integrity is improving user confidence in the machine. This is something
that OSes should have done years ago. All any user ever does on a machine is
manipulate and work with his personal data. Absolute data integrity should be
paramount to any computing technology.

Alas, it is not, and we all have (hopefully) several backups. Again: Anything
that improves data integrity is improving computing as a whole. I want this.

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dstein
"16 exabytes ought to be enough for anybody"

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dhess
> _"There's a huge chasm between using Xsan over Fibre Channel and a USB drive
> with Time Machine," Brady told Ars. "That middle piece is what we're looking
> at—users that want the convenience of a device like a Drobo, but with more
> reliability and [easy verifiability]."_

So, ultimately, this is a hardware play, then. That makes sense, because most
of the features of ZFS don't add any value to a Mac with a single internal
drive and at most one or two USB drives, which is how almost all Macs are
used.

~~~
ssmoot
Except you could do better-than-time-machine, cheap, continuous replication.

You could even TimeMachine-without-additional-drives... I mean, why should my
snapshot system and my backup system be one? How about letting me use
TimeMachine locally, and if I plug up an additional drive, TimeMachine asks me
if I want to backup to it as well?

Not a game-changer exactly, but a nice-ish upgrade potentially.

The biggest upgrade would honestly just be quicker/continuous replication that
doesn't drag the rest of your system down.

~~~
dhess
> _You could even TimeMachine-without-additional-drives... I mean, why should
> my snapshot system and my backup system be one? How about letting me use
> TimeMachine locally, and if I plug up an additional drive, TimeMachine asks
> me if I want to backup to it as well?_

Unless something changes between now and RTM, Lion will provide that feature
out of the box:

[http://www.9to5mac.com/54117/time-machine-can-be-used-
withou...](http://www.9to5mac.com/54117/time-machine-can-be-used-without-an-
external-hard-drive-in-lion/)

And that's about the only feature that a typical Mac user would benefit from
with ZFS, without some kind of "prosumer" or "enterprise-y" external storage
device.

~~~
ssmoot
I almost always use lzjb compression. It's nearly free and gives good returns
for mixed data like the sort you'll find on system drives. Binaries, text,
etc.

Also the reliability aspect. I haven't had HFS+ go bad on my own systems, but
I've seen it several times on servers. It's on about the same level as ext3fs
in that arena, which is pretty bad in my book.

I get the "less is more" argument and I agree generally. ZFS is so far beyond
a traditional FS though.

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riobard
Does ZFS do anything to optimize for SSDs?

~~~
dprice1
There are three ways you can use SSDs with ZFS. First, you can use SSDs in
place of rotating rust. Second, as was previously mentioned, you can use an
SSD as an extension of your filesystem cache. That's called Level-2 Adaptive
Replacement Cache (L2ARC). You can also use an SSD as a logging disk to
accelerate writes; that's called "Logzilla", IIRC.

In commercial offerings built around these features, you typically source an
SSD that is either write-biased (logzilla) or read-biased, depending on what
you are trying to do.

~~~
zdw
Just some formal clarifications:

Logzilla's formal name is ZIL, ZFS Intent Log. Generally these are SLC flash
SSD's, mirrored as losing the ZIL on a ZFS pool can lead to "interesting"
recovery situations.

L2ARC is basically an extension of main memory used to cache data from the
drives. If you lose L2ARC, there aren't any serious consequences. Usually
L2ARC is implemented with less expensive MLC flash SSD's.

On a related note, Seagate sells a Hybrid SSD+rust drive called the Momentus
XT which uses it's 4GB of flash a similar manner to the L2ARC.

~~~
ssmoot
I'm pretty sure the ZIL is not mirrored. If it were, it wouldn't increase
performance since you'd still have to wait for the disks to fsync their copy
to guarantee reliability.

This is why Sun Storage products (and Nexenta, or homegrown clusters) put the
ZIL SSDs in the JBODs and not the storage heads.

You could of-course create a pool that did use a disk as the ZIL, but again,
there'd be no point since the mirror has to be kept consistent otherwise it's
worthless.

Since the cache (L2ARC) is just cache, and you can lose it at anytime without
data-loss, it _is_ in the heads.

Nit-picking. To be clear, the ZIL can (and should be) mirrored, you just want
to do it with SSDs consistently. Mixing devices is possible, but you'll be
limited to the performance of the slowest device. You can also create storage
clusters with multiple heads. Again, a good idea IMO, but the ZIL is a
critical component of the FS. If you lose it, you lose the whole pool (as a
rule I think, but there might be clever hacks around that under special
circumstances if you're lucky). So if you're going to multi-home your zpool,
make sure the ZILs are in the shared-storage region. It's no good having
redundant controllers if your ZIL is on the dead one.

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mttwrnr
We've seen in the past that Apple is willing to adopt superior technology.
They saw the potential of adopting a unix system as well as adopting an Intel
chip. This allows them to provide the same user experience while providing
those users with power, should they want it.

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lutorm
Nice. I just started using zfs on a home linux server. We have some large
Macs, too, it would be nice to have better data integrity there.

~~~
calloc
Try it on FreeBSD or Solaris 11, in general I have found it to perform better
on the same hardware.

~~~
scrod
After many many disk benchmarks, we eventually found that ZFS had the best
performance of all the other included file systems on the latest version
FreeBSD. I highly recommend the combination.

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pstuart
Now Apple just has to buy them and make it standard.

~~~
wmf
I think the article explains why this isn't going to happen.

