[linux-lvm] Reserve space for specific thin logical volumes

[Eric Ren]

Hi Zdenek,

> lvm2 is using  upstream community BZ located here:
>
> https://bugzilla.redhat.com/enter_bug.cgi?product=LVM%20and%20device-mapper 
>
>
> You can check RHBZ easily for all lvm2 bZ
> (mixes  RHEL/Fedora/Upstream)
>
> We usually want to have upstream BZ being linked with Community BZ,
> but sometimes it's driven through other channel - not ideal - but 
> still easily search-able.

Yes, it's a place where problems are discussed. Thanks for your reminder :)

> [...snip...]
> It's should be opposite case - unless something regressed recently...
> Easiest is to write out  lvm2 test suite some test.
>
> And eventually bisect which commit broke it...

Good to know! I will find time to test different versions on both 
openSUSE and Fedora.

>
>> - pvmove is slow. I know it's not fault of LVM. The time is almost 
>> spent in DM (the IO dispatch/copy).
>
> Yeah - this is more or less design issue inside kernel - there are
> some workarounds - but since primary motivation was not to overload
> system - it's been left a sleep a bit - since focus gained  'raid' target

Aha, it's a good reason. Ideally, it would be good for pvmove having 
some option to control
the IO rate. I know it's not easy...

> and these pvmove fixes are working with old dm mirror target...
> (i.e. try to use bigger  region_size for mirror in lvm.conf  (over 512K)
> and evaluate performance  - there is something wrong - but core mirror 
> developer is busy with raid features ATM....

Thanks for the suggestion.

>
>
>> - snapshot cannot be used in cluster environment. There is a usecase: 
>> user has a central backup system
>
> Well, snapshot CANNOT work in cluster.
> What you can do is to split snapshot and attach it different volume,
> but exclusive assess is simply required - there is no synchronization 
> of changes like with cmirrord for old mirror....

Got it! Advanced features like snapshot/thinp/dmcache, have their own 
metadata. The payment for having those metadata
changes cluster-aware is painful.

> We do our best....

Like you guys have been always doing, thanks!

Regards,
Eric