On Sat, Nov 10, 2012 at 5:04 PM, Tim Cook <t...@cook.ms> wrote:
> On Sat, Nov 10, 2012 at 9:59 AM, Jan Owoc <jso...@gmail.com> wrote:
>> Apparently the currently-suggested way (at least in OpenIndiana) is to:
>> 1) create a zpool on the 4k-native drive
>> 2) zfs send | zfs receive the data
>> 3) mirror back onto the non-4k drive
>> I can't test it at the moment on my setup - has anyone tested this to
>> work?
> That would absolutely work, but it's not really a fix for this situation.
> For OP to do this he'd need 42 new drives (or at least enough drives to
> provide the same capacity as what he's using) to mirror to and then mirror
> back.  The only way this is happening for most people is if they only have a
> very small pool, and have the ability to add an equal amount of storage to
> dump to.  Probably not a big deal if you've only got a handful of drives, or
> if the drives you have are small and you can take downtime.  Likely
> impossible for OP with 42 large drives.

Well, if I have to migrate, I basically have three alternatives:

1. safe way:
  a) buy 24 4TB drives,
  b) migrate everything

2. scary way
  a) buy 6 4TB drives,
  b) migrate about 12TB data to new pool
  c) split all mirror vdevs on old pool, add 4k discs to new pool
  d) migrate remaining data to new pool while holding my breath
  e) destroy old pool and reattach discs to vdevs in new pool

3. slightly less scary way
  a) buy 23 3TB drives
  b) set up new pool with 4x mirrored vdevs and 15x non-redundant vdevs
  c) migrate everything from old pool
  d) detatch 3TB discs from mirrors in old pool and attach to vdevs in new pool

I've got room for the first method, but it'll be prohibitively
expensive, even if I sell the old drives. Until 4TB drives drop below
$100 this won't be a realistic option. I don't think I've got the
nerves to do it the scary way :) The third option is a lot cheaper
than the first, but it'll still be a solid chunk of money, so I'll
probably have to think about that for a bit.

That said, I've already migrated far too many times already. I really,
really don't want to migrate the pool again, if it can be avoided.
I've already migrated from raidz1 to raidz2 and then from raidz2 to
mirror vdevs. Then, even though I already had a mix of 512b and 4k
discs in the pool, when I bought new 3TBĀ discs, I couldn't add them to
the pool, and I had to set up a new pool with ashift=12. In
retrospect, I should have built the new pool without the 2TB drives,
and had I known what I do now, I would definately have done that.

Trond Michelsen
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