[OpenIndiana-discuss] Zfs stability "Scrubs"

Michael Stapleton michael.stapleton at techsologic.com
Fri Oct 12 21:07:04 UTC 2012

It is easy to understand that zfs srubs can be useful, But, How often do
we scrub or the equivalent of any other file system? UFS? VXFS?
NTFS? ...
ZFS has scrubs as a feature, but is it a need? I do not think so. Other
file systems accept the risk, mostly because they can not really do
anything if there were errors.
It does no harm to do periodic scrubs, but I would not recommend doing
them often or even at all if scrubs get in the way of production.
What is the real risk of not doing scrubs? 

Risk can not be eliminated, and we have to accept some risk.

For example, data deduplication uses digests on data to detect
duplication. Most dedup systems assume that if the digest is the same
for two pieces of data, then the data must be the same.
This assumption is not actually true. Two differing pieces of data can
have the same digest, but the chance of this happening is so low that
the risk is accepted.

I'm only writing this because I get the feeling some people think scrubs
are a need. Maybe people associate doing scrubs with something like
doing NTFS defrags?

Just my 2 cents!


On Fri, 2012-10-12 at 16:41 -0400, Doug Hughes wrote:

> yes, you shoud do a scrub  and no, there isn't very much risk to this. This
> will scan your disks for bits that have gone stale or the like. You should
> do it. We do a scrub once per week.
> On Fri, Oct 12, 2012 at 3:55 PM, Roel_D <openindiana at out-side.nl> wrote:
> > Being on the list and reading all ZFS problem and question posts makes me
> > a little scared.
> >
> > I have 4 Sun X4140 servers running in the field for 4 years now and they
> > all have ZFS mirrors (2x HD). They are running Solaris 10 and 1 is running
> > solaris 11. I also have some other servers running OI, also with ZFS.
> >
> > The Solaris servers N E V E R had any ZFS scrub. I didn't even knew such
> > existed ;-)
> >
> > Since it all worked flawless for years now i am a huge Solaris/OI fan.
> >
> > But how stable are things nowaday? Does one need to do a scrub? Or a
> > resilver?
> >
> > How come i see so much ZFS trouble?
> >
> >
> >
> > Kind regards,
> >
> > The out-side
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> >
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