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
Regards,
Zhiyong
在 1/4/23 10:09 PM, Zdenek Kabelac 写道:
Dne 04. 01. 23 v 9:00 Zhiyong Ye napsal(a):
Dear all,
The current standard lv implementation of snapshots is COW
(Copy-on-write), which creates snapshots very quickly. However, the
first write performance of the original lv will be poor after creating
a snapshot because of COW. Moreover, the more snapshots there are, the
worse the performance of the original lv will be.
I tested the random read/write performance when the original lv was
created with different number of snapshots. The data is shown below:
Number of snapshots Randread(iops) Randwrite(iops)
0 21989 22034
1 10048 10041
2 6770 6773
3 5375 5378
There are scenarios where the performance of the original lv is more
demanding, and the speed of snapshot creation is not as strong a
requirement. Because it is the original lv that will actually be used,
and the snapshot is only a secondary function. Therefore snapshots
using the COW approach will not meet the needs of this scenario.
Therefore, is it feasible to implement another way of taking
snapshots? Let's say the first snapshot is created as a full snapshot,
and all subsequent snapshots are based on incremental data from the
previous snapshot.
Hi
Have you played with thin provisioning - as that's the answer to the
slow snapshots.
Regards
Zdenek
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