[linux-lvm] New features for using lvm on shared storage

[Eric Ren]

Hi David!

On 01/10/2017 11:30 PM, David Teigland wrote:
> On Tue, Jan 10, 2017 at 09:02:36PM +0800, Eric Ren wrote:
>> Hi David,
>>
>> Sorry for faking this reply because I'm not in the maillist before I noticed
>> this email (quoted blow) you posted for a while.
>>
>> I have a questions about "lvmlockd":
>>
>> Besides clvmd cannot be used together with lvmetad, is there any other
>> main differences between "lvmetad" and "clvmd"? Do you recommend we replace
>> "clvmd" with "lvmetad"?
> Hi, I think you're looking at the differences between lvmlockd and clvmd.
> They have a completely different design and implementation, with lvmlockd
> being much simpler and more obvious in what it does and how it works.
> clvm was sort of designed around the old concept of a "single system
> image" across a cluster, and tried hard to hide any difference between
> local/shared VGs.  lvmlockd just inserts lock/unlock around disk
> modifications when the VG is shared.  And as mentioned before, lvmlockd
> can use sanlock which opens it up to new uses where a cluster doesn't fit.
> I recommend replacing clvm with lvmlockd; I think it works better, and
> clvm will eventually be phased out.
>
> (lvmetad, the metadata caching daemon, can indeed be used with lvmlockd,
> and not clvmd, but this is not a big advantage.  The metadata caching has
> not turned out to be much of a benefit.)

I can always get clear answer and sufficient information of the background from you!

Thanks,
Eric

>
>> """
>>
>> For people using LVM (or clvm) on shared storage, I encourage you to take
>> a look at two recent additions that you may find to be an improvement:
>>
>> 1. System ID
>>
>> is for static ownership of VGs by hosts:
>> http://man7.org/linux/man-pages/man7/lvmsystemid.7.html
>>
>> The nearest equivalent to system ID in the past has been configuring
>> lvm.conf filters uniquely on each host.
>>
>> 2. lvmlockd
>>
>> is for dynamically sharing VGs among hosts:
>> http://man7.org/linux/man-pages/man8/lvmlockd.8.html
>>
>> Using lvmlockd with dlm is similar to what clvmd has done in the past.
>> Using lvmlockd with sanlock has no prior equivalent.
>>
>> (For distribution packaging, see the "lvm2-lockd" rpm.)
>>
>> Dave
>> """