[linux-lvm] Snapshot behavior on classic LVM vs ThinLVM

[Zdenek Kabelac]

Dne 1.3.2018 v 13:48 Gionatan Danti napsal(a):
> 
> On 01/03/2018 12:23, Zdenek Kabelac wrote:
>> In general - for extX  it's remount read-only upon error - which works for 
>> journaled metadata - if you want same protection for 'data' you need to 
>> switch to rather expensive data journaling mode.
>>
>> For XFS there is now similar logic where write error on journal stops 
>> filesystem usage - look far some older message (even here in this list) it's 
>> been mentioned already few times I guess...
> 

There is quite 'detailed' config for XFS - just not all settings
are probably tuned in the best way for provisioning.

See:


https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/xfs-error-behavior


> 
>> Unfreezed filesystem is simply not usable...
> 
> I was speaking about unfreezed thin metadata snapshot - ie: 
> reserve_metadata_snap *without* a corresponding release_metadata_snap. Will 
> that cause problems?
> 

metadata snapshot 'just consumes' thin-pool metadata space,
at any time there can be only 1 snapshot - so before next usage
you have to drop the existing one.

So IMHO it should have no other effects unless you hit some bugs...

> I think VDO is a fruit of Permabit acquisition, right? As it implements it's 
> own thin provisioning, will thinlvm migrate to VDO or it will continue to use 
> the current dmtarget?


thin-pool  target is having different goals then VDO
so both targets will likely live together.

Possibly thin-pool might be tested for using VDO data volume if it makes any 
sense...

Regards

Zdenek