[OpenIndiana-discuss] Zfs stability "Scrubs"

Heinrich van Riel heinrich.vanriel at gmail.com
Mon Oct 15 23:57:28 UTC 2012

On Mon, Oct 15, 2012 at 6:21 PM, Jason Matthews <jason at broken.net> wrote:

> From: heinrich.vanriel at gmail.com [mailto:heinrich.vanriel at gmail.com]
> > My point is most high end storage units has some form of data
> > verification process that is active all the time.
> As does ZFS. The blocks are checksumed on each read. Assuming you have
> mirrors or parity redundancy, the misbehaving block is corrected,
> reallocated, etc.
> Right, I understand ZFS checks data on each read, my point is checking the
disk or data periodically.

> In my opinion scrubs should be considered depending on the importance
> > of data and the frequency based on what type of raidz, change rates
> > and disk type used.
> One point of scrubs is to verify the data that you don't normally read.
> Otherwise, the errors would be found in real time upon the next read.

Understood, if full backups are executed weekly/monthly no scrub is

> > Perhaps in future ZFS will have the ability to limit resource
> > allocation when scrubbing like with BV where it can be set. Rebuild
> > priory can also be set.
> There are tunables for this.
> Thanks, did not know will research, had a fairly heavy impact the other
day replacing a disk..

> > Also some high end controllers have "port" verify for each
> > disk (media read) when using their integrated raid that runs
> > periodically. Since in the world of ZFS it is recommended to use
> > JBOD I see it as more than just the filesystem. I have never deployed
> > a system containing mission critical data using filesystem raid
> > protection other than with ZFS since there is no protection in them an
> > I would much rather bank on the controller.
> Unfortunately my parser was unable to grok this. Seems like you would
> prefer
> a raid controller.

Sorry, boils down to this, if ZFS is not an option I use a raid controller
if data is important.
In fact I do not like to be tied to a specific controller, zfs gives me the
freedom to change at any point

> j.
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