Re: fdisk(8) vs gpart(8), and gnop

On 06/02/14 10:15, Justin T. Gibbs wrote:
> On Jun 2, 2014, at 9:49 AM, Mark Felder <feld@FreeBSD.org> wrote:
>
>> On 2014-06-02 10:02, Nathan Whitehorn wrote:
>>> My bigger concern is this pool upgrade one -- what if someone puts in
>>> a 4K disk in the future?
>> This is a concern of mine, and I sort of wish we did 4k by default and f=
orced people to override if they want 512b or something else.
> Adding a 4k sectored device is fine.  You just need to use it in a new to=
p-level vdev in the pool.
>
> If you are at the point where you can=92t get new or compatible warrantee=
 replacements for the drives that may fail in your existing pool, you shoul=
d be migrating your data to new devices anyway.  Mixing devices with differ=
ent performance characteristics within a TLV can lead to pessimal behavior.=
  I don=92t think that ZFS should jump through large hoops to try and make =
this work well.  Instead, we should encourage the use of similar devices wi=
thin a TLV (guidance that the installer has sufficient information to provi=
de*) and the system should be optimized assuming this is how it will be use=
d.
>
> I certainly *do not* want FreeBSD to automatically inflate the ashift use=
d on my pools.  Doing so is an attempt to guess why I chose the devices I d=
id at pool creation time and my strategy for retiring them in the future.  =
The current proposal guesses wrong for me and the products I help build.  I=
=92d bet it will be wrong more times than right.
>
> =97
> Justin
>
> *) Using the tools already in FreeBSD it is quite easy to group devices b=
y transport type, capacity, logical block size, physical block size, and, f=
or at least SCSI transports, media rotational speed.  We do this in Spectra=
=92s ZFS appliance so users have to work really hard to mix devices that th=
ey shouldn=92t.
>
Well, this makes it sound easy then. We just don't worry about it and =

keep the existing defaults. This requires some documentation updates and =

changes to the installer. The "standard" advice seems to be universally =

to add gnops to set the sector size to 4k and the existing installer ZFS =

support does this.
-Nathan
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