> From: Sašo Kiselkov [mailto:skiselkov...@gmail.com]
> as far as incompatibility among products, I've yet to come
> across it

I was talking about ... install solaris 11, and it's using a new version of zfs 
that's incompatible with anything else out there.  And vice-versa.  (Not sure 
if feature flags is the default, or zpool 28 is the default, in various 
illumos-based distributions.  But my understanding is that once you upgrade to 
feature flags, you can't go back to 28.  Which means, mutually, anything >28 is 
incompatible with each other.)  You have to typically make a conscious decision 
and plan ahead, and intentionally go to zpool 28 and no higher, if you want 
compatibility between systems.

> Let us know at z...@lists.illumos.org how that goes, perhaps write a blog
> post about your observations. I'm sure the BTRFS folks came up with some
> neat ideas which we might learn from.

Actually - I've written about it before (but it'll be difficult to find, and 
nothing earth shattering, so not worth the search.)  I don't think there's 
anything that zfs developers don't already know.  Basic stuff like fsck, and 
ability to shrink and remove devices, those are the things btrfs has and zfs 
doesn't.  (But there's lots more stuff that zfs has and btrfs doesn't.  Just 
making sure my previous comment isn't seen as a criticism of zfs, or a 
judgement in favor of btrfs.)

And even with a new evaluation, the conclusion can't be completely clear, nor 
immediate.  Last evaluation started about 10 months ago, and we kept it in 
production for several weeks or a couple of months, because it appeared to be 
doing everything well.  (Except for features that were known to be not-yet 
implemented, such as read-only snapshots (aka quotas) and btrfs-equivalent of 
"zfs send.")  Problem was, the system was unstable, crashing about once a week. 
 No clues why.  We tried all sorts of things in kernel, hardware, drivers, with 
and without support, to diagnose and capture the cause of the crashes.  Then 
one day, I took a blind stab in the dark (for the ninetieth time) and I 
reformatted the storage volume ext4 instead of btrfs.  After that, no more 
crashes.  That was approx 8 months ago.

I think the only thing I could learn upon a new evaluation is:  #1  I hear 
"btrfs send" is implemented now.  I'd like to see it with my own eyes before I 
believe it.  #2  I hear quotas (read-only snapshots) are implemented now.  
Again, I'd like to see it before I believe it.  #3  Proven stability.  Never 
seen it yet with btrfs.  Want to see it with my eyes and stand the test of time 
before it earns my trust.

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