[linux-lvm] The benefits of lvmlockd over clvmd?
zren at suse.com
Wed Jan 10 07:11:24 UTC 2018
Thanks for your explanations!
On 01/10/2018 12:06 AM, David Teigland wrote:
> On Tue, Jan 09, 2018 at 11:15:24AM +0800, Eric Ren wrote:
>> Hi David,
>> Regarding the question of the subject, I can think of three main benefits of
>> lvmlockd over clvmd:
>> - lvmlockd supports two cluster locking plugins: dlm and sanlock. sanlock
>> plugin can supports up to ~2000 nodes
>> that benefits LVM usage in big virtulizaton/storage cluster,
> True, although it's never been tried anywhere near that many. The main
> point hiding behind the big number is that hosts are pretty much unaware
> of each other, so adding more doesn't have any affect, and when something
> happens to one, others are unaffected because they are unaware.
The comments above is only talking about lvmlockd with sanlock, and it's
because the different protocols/algorithms used by them: sanlock with Paxos,
dlm with corosync, right?
>> while dlm plugin fits HA clsuter.
>> - lvmlockd has better design than clvmd. clvmd is command-line level based
>> locking system, which means the
>> whole LVM software will get hang if any LVM command gets dead-locking
>> issue. However, lvmlockd is *resources* based
>> cluster locking. The resources to protect is VG and LV so that the deadlock
>> issue will be isolated inside the resource and
>> operations on other VG/LV can still proceed.
Is this point roughly true?
>> - lvmlockd can work with lvmetad.
>> But, I may be wrong in some points. Could you please help correct me and
>> complete the benefit list?
> To me the biggest benefit is the design and internal implementation, which
> I admit don't make for great marketing. The design in general follows the
> idea described above, in which hosts fundamentally operate unaware of
Sorry, "the idea described above" by me?
> others and one host never has any effect on another. That's diametrically
For example, with clvmd the command "lvchange -ay VG/LV" will try to
activate the LV
on every hosts, but with lvmlockd, we need to perform "lvchange -asy" on
each host :)
> opposite to the original clvm "single system image" design in which
> everything that happens is in theory meant to be happening everywhere.
Got it. Thanks again.
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