Using the *real* sector/block size of a mass storage device for ZFS

[Dustin Wenz]

Thanks for the information!

I'm curious as to why gnop is the best way to accomplish this... FreeBSD 10 seems to automatically set ashift: 12 when a new vdev is created. I definitely appreciate the control that gnop provides, however.

Am I correct in assuming that it is absolutely impossible to convert an existing ashift:9 vdev to ashift:12? Some of my pools are approaching 1PB in size; transferring the data off and back again would be inconvenient.

I suppose I should just be thankful that ZFS is warning me about this now, before I need to build any really large storage pools. 

	- .Dustin

On Feb 7, 2014, at 3:23 PM, Mark Felder <feld at freebsd.org> wrote:

> 
> 
> On Fri, Feb 7, 2014, at 14:44, Dustin Wenz wrote:
>> We have been upgrading systems from FreeBSD 9.2 to 10.0-RELEASE, and I'm
>> noticing that all of my zpools now show this status: "One or more devices
>> are configured to use a non-native block size. Expect reduced
>> performance." Specifically, each disk reports: "block size: 512B
>> configured, 4096B native".
>> 
>> I've checked these disks with diskinfo and smartctl, and they report a
>> sector size of 512B. I understand that modern disks often use larger
>> sectors due to addressing limits, but I'm unsure how ZFS can disagree
>> with these other tools.
>> 
>> In any case, it looks like I will need to rebuild every zpool. There are
>> many thousands of disks involved and the process will take months (if not
>> years). How can I be I sure that this is done correctly this time? Will
>> ZFS automatically choose the correct block size, assuming that it's
>> really capable of this?
>> 
>> In the meantime, how can I turn off that warning message on all of my
>> disks? "zpool status -x" is almost worthless due to the extreme number of
>> errors reported.
>> 
> 
> ZFS is doing the right thing by telling you that you should expect
> degraded performance. The best way to fix this is to use the gnop method
> when you build your zpools:
> 
> gnop create -S 4096 /dev/da0
> gnop create -S 4096 /dev/da1
> zpool create data mirror /dev/da0.nop /dev/da1.nop
> 
> Next reboot or import of the zpool will use the regular device names
> with the correct ashift for 4K drives.
> 
> The drive manufacturers handled this transition extremely poorly.
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