[rescue] Solaris ZFS questions

Zachary Giles zgiles at gmail.com
Wed Jan 19 16:29:10 CST 2011

So it's a verification of all the checksums etc which means you might find
an error sooner rather than later if your checksums dont match (and it will
fix it if it can). But, I also thought that one of the nice features of ZFS
is that it does continuous checksumming.

>From Wikipedia (not the best source..but it's ok):
"ZFS uses a copy-on-write transactional object model. All block pointers
within the filesystem contain a 32-bit checksum or 256-bit hash [shortened]
of the target block which is verified when the block is read."

Sounds like If you access a file, it checks the sum. Looks like the only
reason to do a scrub is to find out sooner. If there are errors, it will fix
them if it's a scrub or a read, and probably report neither if it's
correctable. Is that right?

Didnt mean to hijack the thread.. but it is about ZFS.. sorry I it's a
problem... Just looking to understand a little better.

On Wed, Jan 19, 2011 at 3:06 PM, Phil Stracchino <alaric at metrocast.net>wrote:

> On 01/19/11 16:22, Zachary Giles wrote:
> > So, this might be a silly question, but what does zpool scrub do? Is
> > your data not safe until then?
> Briefly, zpool scrub checks the status of the pool and the integrity of
> the devices and data.
> "Another reliability feature of ZFS pools is data scrubbing. One problem
> with traditional file systems is that the reliability of any data that s
> not referenced by the system s normal operation is unknown; you may have
> errors that are silently lying in wait to be found when the data is
> actually needed. To combat this hazard, ZFS provides a data-scrubbing
> feature to verify the integrity of every block of data in a pool. During
> a scrub operation, ZFS reads each block and verifies
> it against its checksum. If it finds an error on a device that is part
> of a mirror or raidz device, ZFS attempts to repair the block;
> otherwise, the error is reported."
> --
>  Phil Stracchino, CDK#2     DoD#299792458     ICBM: 43.5607, -71.355
>  alaric at caerllewys.net   alaric at metrocast.net   phil at co.ordinate.org
>         Renaissance Man, Unix ronin, Perl hacker, Free Stater
>                 It's not the years, it's the mileage.
> _______________________________________________
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Zach Giles
zgiles at gmail.com

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