On 2012-12-21 11:28, Arthur Chance wrote:
On 12/21/12 14:06, Paul Kraus wrote:
On Dec 21, 2012, at 7:49 AM, yudi v wrote:
I am building a new freebsd fileserver to use for backups, will be
using 2
disk raid mirroring in a HP microserver n40l.
I have gone through some of the documentation and would like to
know what
file systems to choose.
According to the docs, ufs is suggested for the system partitions
but
someone on the freebsd irc channel suggested using zfs for the
rootfs as
well
Are there any disadvantages of using zfs for the whole system
rather than
going with ufs for the system files and zfs for the user data?
First a disclaimer, I have been working with Solaris since 1995 and
managed
lots of data under ZFS, I have only been working with FreeBSD for
about the past
6 months.
UFS is clearly very stable and solid, but to get redundancy you
need to use
a separate volume manager.
Slight correction here - you don't need a volume manager (as I
understand the term), you'd use the GEOM subsystem, specifically
gmirror in this case. See man gmirror for details
ZFS is a completely different way of thinking about managing
storage (not
just a filesystem). I prefer ZFS for a number of reasons:
1) End to end data integrity through checksums. With the advent of 1
TB plus
drives, the uncorrectable error rate (typically 10^-14 or 10^-15)
means that
over the life of any drive you *are* now likely to run into
uncorrectable errors.
This means that traditional volume managers (which rely on the drive
reporting an
bad reads and writes) cannot detect these errors and bad data will
be returned to
the application.
2) Simplicity of management. Since the volume management and
filesystem layers
have been combined, you don't have to manage each separately.
3) Flexibility of storage. Once you build a zpool, the filesystems
that reside
on it share the storage of the entire zpool. This means you don't
have to decide
how much space to commit to a given filesystem at creation. It also
means that all
the filesystems residing in that one zpool share the performance of
all the drives
in that zpool.
4) Specific to booting off of a ZFS, if you move drives around (as I
tend to do in
at least one of my lab systems) the bootloader can still find the
root filesystem
under ZFS as it refers to it by zfs device name, not physical drive
device name.
Yes, you can tell the bootloader where to find root if you move it,
but zfs does
that automatically.
5) Zero performance penalty snapshots. The only cost to snapshots is
the space
necessary to hold the data. I have managed systems with over 100,000
snapshots.
I am running two production, one lab, and a bunch of VBox VMs all
with ZFS.
The only issue I have seen is one I have also seen under Solaris
with ZFS. Certain
kinds of hardware layer faults will cause the zfs management tools
(the zpool and
zfs commands) to hang waiting on a blocking I/O that will never
return. The data
continuos to be available, you just can't manage the zfs
infrastructure until the
device issues are cleared. For example, if you remove a USB drive
that hosts a
mounted ZFS, then any attempt to manage that ZFS device will hang
(zpool export
-f zpool name hangs until a reboot).
Previously I had been running (at home) a fileserver under
OpenSolaris using
ZFS and it saved my data when I had multiple drive failures. At a
certain client
we had a 45 TB configuration built on top of 120 750GB drives. We
had multiple
redundancy and could survive a complete failure of 2 of the 5 disk
enclosures (yes,
we tested this in pre-production).
There are a number of good writeups on how setup a FreeBSD system
to boot off
of ZFS, I like this one the best
http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/9.0-RELEASE , but I do
the zpool/zfs
configuration slightly differently (based on some hard learned
lessons on Solaris).
I am writing up my configuration (and why I do it this way), but it
is not ready yet.
Make sure you look at all the information here:
http://wiki.freebsd.org/ZFS ,
keeping in mind that lots of it was written before FreeBSD 9. I
would NOT use ZFS,
especially for booting, prior to release 9 of FreeBSD. Some of the
reason for this
is the bugs that were fixed in zpool version 28 (included in release
9).
I would agree with all that. My current system uses UFS filesystems
for the base install, and ZFS with a raidz zpool for everything else,
but that's only because I started using ZFS in REL 8.0 when it was
just out of experimental status, and I didn't want to risk having an
unbootable system. (That last paragraph suggests I was wise in that
decision.) My next machine I'm specing out now will be pure ZFS so I
get the boot environment stuff.
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