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

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 fo=
rced 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 top-=
level vdev in the pool.

If you are at the point where you can=92t get new or compatible warrantee r=
eplacements for the drives that may fail in your existing pool, you should =
be migrating your data to new devices anyway.  Mixing devices with differen=
t 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 th=
is work well.  Instead, we should encourage the use of similar devices with=
in a TLV (guidance that the installer has sufficient information to provide=
*) and the system should be optimized assuming this is how it will be used.

I certainly *do not* want FreeBSD to automatically inflate the ashift used =
on my pools.  Doing so is an attempt to guess why I chose the devices I did=
 at pool creation time and my strategy for retiring them in the future.  Th=
e 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 by =
transport type, capacity, logical block size, physical block size, and, for=
 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.
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