RFC: Suggesting ZFS "best practices" in FreeBSD

[Freddie Cash]

On Jan 22, 2013 7:04 AM, "Warren Block" <wblock at wonkity.com> wrote:
>
> On Tue, 22 Jan 2013, Borja Marcos wrote:
>
>> 1- Dynamic disk naming -> We should use static naming (GPT labels, for
instance)
>>
>> ZFS was born in a system with static device naming (Solaris). When you
plug a disk it gets a fixed name. As far as I know, at least from my
experience with Sun boxes, c1t3d12 is always c1t3d12. FreeBSD's dynamic
naming can be very problematic.
>>
>> For example, imagine that I have 16 disks, da0 to da15. One of them,
say, da5, dies. When I reboot the machine, all the devices from da6 to da15
will be renamed to the device number -1. Potential for trouble as a minimum.
>>
>> After several different installations, I am preferring to rely on static
naming. Doing it with some care can really help to make pools portable from
one system to another. I create a GPT partition in each drive, and Iabel it
with a readable name. Thus, imagine I label each big partition (which takes
the whole available space) as pool-vdev-disk, for example,
pool-raidz1-disk1.
>
>
> I'm a proponent of using various types of labels, but my impression after
a recent experience was that ZFS metadata was enough to identify the drives
even if they were moved around.  That is, ZFS bare metadata on a drive with
no other partitioning or labels.
>
> Is that incorrect?

The ZFS metadata on disk allows you to move disks around in a system and
still import the pool, correct.

But the ZFS metadata will not help you figure out which disk, in which bay,
of which drive shelf just died and needs to be replaced.

That's where glabels, gpt labels, and similar come in handy. It's for the
sysadmin, not the system itself.