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Description of problem:
the data percent of thin snapshots is not same after doing discards.


Version-Release number of selected component (if applicable):
lvm2-2.02.98-5.el7.x86_64
kernel-3.9.0-0.rc6.51.el7.x86_64

How reproducible:


Steps to Reproduce:
1. create multiple snapshots of the same origin thin LV
2. do fstrim on the snapshots
3. lvs
  
Actual results:
the data percent of the snapshots is not same.

[CMD][00:48:53][dhcp-13-131.nay.redhat.com]lvs tsvg -o+discards
STDOUT:
  LV     VG   Attr      LSize   Pool Origin Data%  Move Log Copy%  Convert Discards
  origin tsvg Vwi-aotz- 100.00m pool         67.94                         nopassdown
  pool   tsvg twi-a-tz- 500.00m              15.59                         nopassdown
  snap1  tsvg Vwi-a-tz- 100.00m pool origin   8.19                         nopassdown
  snap2  tsvg Vwi-a-tz- 100.00m pool origin   8.19                         nopassdown
  snap3  tsvg Vwi-a-tz- 100.00m pool origin   7.06                         nopassdown
  snap4  tsvg Vwi-aotz- 100.00m pool origin   6.31                         nopassdown
  snap5  tsvg Vwi-a-tz- 100.00m pool origin  65.38                         nopassdown
STDERR:
RETURN:0


Expected results:


Additional info:

Created attachment 736670 [details]
test.log

very slight difference, not sure if it's by design.