On 20-Jun-07, at 12:23 PM, Richard L. Hamilton wrote:
Hello,
I'm quite interested in ZFS, like everybody else I
suppose, and am about
to install FBSD with ZFS.
On that note, i have a different first question to
start with. I
personally am a Linux fanboy, and would love to
see/use ZFS on linux. I
assume that I can use those ZFS disks later with any
os that can
work/recognizes ZFS correct? e.g. I can
install/setup ZFS in FBSD, and
later use it in OpenSolaris/Linux Fuse(native) later?
I've seen some discussions that implied adding attributes
to support non-Solaris (*BSD) uses of zfs, so that the format would
remain interoperable (i.e. free of incompatible extensions),
although not all OSs might fully support those. But I don't know
if there's some firm direction to keeping the on-disk format
compatible across platforms that zfs is ported to. Indeed, if the
code is open-source, I'm not sure that's possible to _enforce_. But
I suspect (and certainly hope) it's being encouraged. If someone who
works on zfs could comment on that, it might help.
Mat Ahrens recently did, on this list:
... as a leader of Sun's ZFS team, and the OpenSolaris ZFS
community, I would do everything in my power to prevent the ZFS on-
disk format from diverging in different implementations. Let's
discuss the issues on this mailing list as they come up, and try to
arrive at a conclusion which offers the best ZFS for *all* ZFS
users, OpenSolaris or otherwise.
...
FYI, we're already working with engineers on some other ports to
ensure on-disk compatability. Those changes are going smoothly.
So please, contact us if you want to make (or want us to make) on-
disk changes to ZFS for your port or distro. We aren't that
difficult to work with :-)
--mat
--Toby
Anyway, back to business :)
I have a whole bunch of different sized disks/speeds.
E.g. 3 300GB disks
@ 40mb, a 320GB disk @ 60mb/s, 3 120gb disks @ 50mb/s
and so on.
Raid-Z and ZFS claims to be uber scalable and all
that, but would it
'just work' with a setup like that too?
I used to match up partition sizes in linux, so make
the 320gb disk into
2 partitions of 300 and 20gb, then use the 4 300gb
partitions as a
raid5, same with the 120 gigs and use the scrap on
those aswell, finally
stiching everything together with LVM2. I can't easly
find how this
would work with raid-Z/ZFS, e.g. can I really just
put all these disks
in 1 big pool and remove/add to it at will? And I
really don't need to
use softwareraid yet still have the same reliablity
with raid-z as I had
with raid-5? What about hardware raid controllers,
just use it as a JBOD
device, or would I use it to match up disk sizes in
raid0 stripes (e.g.
the 3x 120gb to make a 360 raid0).
Or you'd recommend to just stick with
raid/lvm/reiserfs and use that.
One of the advantages of zfs is said to be that if it's used
end-to-end, it can catch more potential data integrity issues
(including controller, disk, cabling glitches, misdirected writes,
etc).
As far as I understand, raid-z is like raid-5 except that the stripes
are varying size, so all writes are full-stripe, closing the "write
hole",
so no NVRAM is needed to ensure that recovery would always be
possible.
Components of raid-z or raid-z2 or mirrors can AFAIK only be used
up to the
size of the smallest component. However, a zpool can consist of
the aggregation (dynamic striping, I think) of various mirrors or
raid-z[2]
virtual devices. So you could group similar sized chunks (be it
partitions or
whole disks) into redundant virtual devices, and aggregate them all
into a
zpool (and add more later to grow it, too). Ideally, all such
virtual devices
would have the same level of redundancy; I don't think that's
_required_, but
there isn't much good excuse for doing otherwise, since the
performance of
raid-z[2] is different from that of a mirror.
There may be some advantages to giving zfs entire disks where
possible;
it will handle labelling (using EFI labels) and IIRC, may be able
to better
manage the disk's write cache.
For the most part, I can't see many cases where using zfs together
with
something else (like vxvm or lvm) would make much sense. One possible
exception might be AVS (http://opensolaris.org/os/project/avs/) for
geographic redundancy; see http://blogs.sun.com/AVS/entry/
avs_and_zfs_seamless
for more details.
It can be quite easy to use, with only two commands (zpool and zfs);
however, you still want to know what you're doing, and there are
plenty of
issues and tradeoffs to consider to get the best out of it.
Look around a little for more info; for example,
http://www.opensolaris.org/os/community/zfs/faq/
http://en.wikipedia.org/wiki/ZFS
http://docs.sun.com/app/docs/doc/817-2271 (ZFS Administration Guide)
http://www.google.com/search?hl=en&q=zpool+OR+zfs+site%
3Ablogs.sun.com&btnG=Search
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