[linux-lvm] The feasibility of implementing an alternative snapshot approach

Zdenek Kabelac zdenek.kabelac at gmail.com
Fri Jan 6 13:42:22 UTC 2023

Dne 04. 01. 23 v 17:12 Zhiyong Ye napsal(a):
> Hi Zdenek,
> Thank you for your reply.
> Snapshots of thinlv are indeed more efficient compared to standard lv, this is 
> because data blocks can be shared between snapshot and original thinlv. But 
> there is also a performance loss after thinlv creates a snapshot. This is 
> because the first write to the snapshotted thinlv requires not only allocating 
> a new chunk but also copying the old data.
> Here are some performance data and a discussion of the thinlv snapshot:
> https://listman.redhat.com/archives/linux-lvm/2022-June/026200.html

Well that's our current  'state-of-the-art' solution.

Make sure you are using latest kernels for your performance testing - there 
have been several improvements around the locking (6+ kernels) - but if this 
still not good enough for your case you might need to seek for some other 
solutions (although would be nice to know who handles this task better).

Definitely the old 'thick-snapshot' is mostly in maintenance phase and it's 
usability (and its design) is limited for some short living temporary 
snapshoting (i.e. you are making backup and after completing your backup of 
the filesystem you remove your temporary snapshot - it's been never designed 
to be used for multi-level multi-GiB snapshots - this will not fly...

When you use thin snapshots - make sure your metadata LV is located on your 
fast device and you use best fitting chunksize.



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