[OpenIndiana-discuss] Zfs stability "Scrubs"

Jason Matthews jason at broken.net
Mon Oct 15 22:21:00 UTC 2012

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.

> 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.

> 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.

> 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.


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