Hi Zdenek,
Thank you for your detailed answer.
For the thin snapshot I will use the latest version of kernel and lvm
for further testing. I want to use both snapshot methods (thin and
thick) in the production environment. But if the thick snapshot is only
still in the maintenance phase, then for thick lv I have to see if there
is any other way to accomplish the snapshot function.
I use lvm mainly for virtualized environments. Each lv acts as a block
device of the virtual machine. So I also consider using qemu's own
snapshot feature. When qemu creates a snapshot, the original image used
by the virtual machine becomes read-only, and all write changes are
stored in the new snapshot. But currently qemu's snapshots only support
files, not block devices.
Regards
Zhiyong
On 1/6/23 9:42 PM, Zdenek Kabelac wrote:
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.
Regards
Zdenek
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