[Discuss] Thin Provisioned LVM

[markw at mohawksoft.com (markw at mohawksoft.com)]

>> From: markw at mohawksoft.com [mailto:markw at mohawksoft.com]
>>
>> >> From: Discuss [mailto:discuss-bounces+blu=nedharvey.com at blu.org] On
>> >> Behalf Of markw at mohawksoft.com
>> >>
>> >> says give ZFS whole disks, which is stupid.
>> >
>> > Mark, clearly you know nothing about ZFS.
>>
>> Think what you wish. Maybe I'm not explaining the problem....
>
> You're explaining your thoughts well - it's just that you're saying a lot
> of things that demonstrate lack of understanding of ZFS.

This is something you've said, but you haven't pointed to anything that is
incorrect. I really hate when people bring a "personal" pejorative to a
technical discussion. The problem I have had with ZFS and its supporters
is that they don't accept their baby is is not perfect and I raised real
issues that real users have, and sink to making it personal, so be it.

Yes, if you put an SSD on the ZIL, you can improve performance, and there
are a host of tricks you can use. If I have not stated it, I will state it
now, ZFS has some features that make it a great system for a broad set of
applications, but it does have issues related to performance and resource
usage that make it unsuitable for some classes of applications and/or
environments. To deny this would be *you* having a lack of understanding
of ZFS or systems design.


> Normally I like
> to react to those kind of things in a helpful manner, but for 1, you're
> certainly writing the stuff much faster than I have time to react to, and
> for 2, based on a zillion similar things you've written here before, I
> believe you have some kind of personal bias that I don't understand,

It isn't personal bias to debate the pros and cons of a system. I'm sorry
if I offend people if I barbecue their sacred cows. ZFS is just a thing
and for the class of systems and environments I deal with, some of its
behaviors run against the design criteria of the rest of the system. A
database-like system that manages its blocks and data integrity will
generally show a degradation in performance on ZFS.

> some
> kind of personal resentment for zfs.  I don't think anything I can say is
> going to change your mind about anything, so it would also be a waste of
> time for me to react to your zfs comments for your sake.

(1) If someone could point me in the direction of documentation on how to
get ZFS to update file or zvol blocks IN PLACE, i.e. without going through
the ZIL, then cool, I would really find that helpful.

(2) If someone could point me to a property of a ZFS pool to favor re-use
of storage blocks rather than expanding the footprint of the zpool usage
on the device, I would find that very helpful.

Both these behaviors REALLY REALLY impact enterprise class systems. Saying
"you are doing it wrong" is not an answer because #1 is a problem for
highly performant data systems and #2 is a problem for IT in corporations
that run SAN environments which use space-efficient (thin provisioned)
volumes.

>I personally
> believe each tool is a tool, and has characteristics different from each
> other, and based on those characteristic differences, each tool is better
> for certain situations.  But as I mentioned, there's *almost* no situation
> I can think of where I would choose lvm over zfs.

First, on Linux, currently, ZFS does not cluster across multiple systems,
so there's one instance. That means you can't create fully redundant
applications on Linux using ZFS.

That combined with my previous issues, really move ZFS out of the running
for a host of "enterprise class" applications.

>
> I only want to tell people "don't listen to what this guy says about zfs.

Now, I seriously take offense too this. If I were to say, Edward Ned
Harvey is an idiot, on the internet, that's bad because it cached and
searchable on google for the rest of time. The ad-hominem attack is the
lowest form of debate and a clear sign that the person using it has no
real standing in the discussion.

You do not know me and have no idea what I do or do not know about
anything, and nothing I have written about ZFS is fundamentally incorrect
at this point in time. You don't even bother to debate it, you just sink
to using insults. Are you comfortable with that level of discourse? I
dislike it. Saying "You are wrong about XYZ, here's why" means that you
can be respectful and have a proper discussion. Saying "I want to tell
people don't listen to this guy" is a personal attack.