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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