zfs discuss - Dec 2010 - Resilvering - Scrubing whats the different

Hello All

I read this thread Resilver/scrub times? for a few minutes
and I have recognize that I dont know the different between
Resilvering and Scrubing. Shame on me. :-(

I dont find some declarations in the man-pages and I know the command
to start scrubing "zpool scrub tank"
but what is the command to start resilver and what is the different?

-- 
Best Regards
Alexander
Dezember, 20 2010

On 12/21/10 08:36 AM, Alexander Lesle wrote:
> Hello All
>
> I read this thread Resilver/scrub times? for a few minutes
> and I have recognize that I dont know the different between
> Resilvering and Scrubing. Shame on me. :-(
>
Scrubbing is used to check the contents of a pool by reading the data 
and verifying its checksum.

To quote the man page:

          Scrubbing and resilvering are very  similar  operations.
          The  difference  is  that resilvering only examines data
          that ZFS knows to be out  of  date  (for  example,  when
          attaching  a  new  device  to  a  mirror or replacing an
          existing device), whereas scrubbing examines all data to
          discover  silent  errors  due to hardware faults or disk
          failure.
> I dont find some declarations in the man-pages and I know the command
> to start scrubing "zpool scrub tank"
> but what is the command to start resilver and what is the different?
>
There isn''t one.  resilvering starts automatically when a dive is
replaced.

-- 
Ian.

On 12/20/2010 11:36 AM, Alexander Lesle wrote:
> Hello All
>
> I read this thread Resilver/scrub times? for a few minutes
> and I have recognize that I dont know the different between
> Resilvering and Scrubing. Shame on me. :-(
>
> I dont find some declarations in the man-pages and I know the command
> to start scrubing "zpool scrub tank"
> but what is the command to start resilver and what is the different?
>
Resilvering is reconstruction of a failed drive (or portion of that 
drive).  It involves walking the metadata tree of the pool, to see if 
all blocks are stored properly on the correct devices; if not, then a 
write is issued to the device which is missing the correct block.  It 
does NOT deal with checksums of the individual blocks.

Scrubbing is error-detection.  Scrubbing looks for blocks whose metadata 
checksums do not match the checksum returned by the data held in the 
block. If the data doesn''t match, ONLY then does a new block get
written
out.

Scrubbing is independent of media failure (that is, it isn''t triggered 
by the failure of block or whole device) - it is performed by a userland 
action.

Resilvering is dependent on device failure (whether permanent, or 
temporary) - it is triggered by a system condition.

-- 
Erik Trimble
Java System Support
Mailstop:  usca22-123
Phone:  x17195
Santa Clara, CA
Timezone: US/Pacific (GMT-0800)

Hello Erik Trimble and Ian Collins,

thx for quick answering.

My inexperience is solved and I am glad.

-- 
Best Regards
Alexander
Dezember, 20 2010
........
[1] mid:4D0FB4A4.1090800 at oracle.com
........