Bug 1805896

Cond. NAK for 8.3 - insufficient description.

This is an internal change to the way lvm flushes data from the cache to the origin.  Since this changes the way writecache is implemented in lvm, not changing this will mean that very few other changes are possible.


writecache: use two stage detach

Avoid flushing, and potentially blocking for a long time,
in suspend by using the cleaner setting.

To detach the writecache, first set the cleaner option on the
writecache LV without detaching the writecache.  Then return
to the top level of the command, releasing the VG and the VG lock.
From there, periodically check the progress of the cleaner by
locking/reading the VG and checking kernel status.  Once the
cleaner has finished flushing, detach the writecache from the LV.

pushed to master
https://sourceware.org/git/?p=lvm2.git;a=commit;h=c32d7fed4f78b4537f4ada4318866786a9fab493

Fix verified in the rpms.

kernel-4.18.0-275.el8    BUILT: Sat Jan 16 06:29:19 CST 2021
lvm2-2.03.11-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021
lvm2-libs-2.03.11-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021
device-mapper-1.02.175-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021
device-mapper-libs-1.02.175-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021
device-mapper-event-1.02.175-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021
device-mapper-event-libs-1.02.175-1.el8    BUILT: Fri Jan  8 05:21:07 CST 2021


# Start writing a bunch of files
[root@hayes-01 ~]#  /usr/tests/sts-rhel8.3/bin/checkit -w /mnt/large_writecache_removal -f /tmp/checkit_origin_1 -n 1200
checkit starting with:
CREATE
Num files:          1200
Random Seed:        3819
Verify XIOR Stream: /tmp/checkit_origin_1
Working dir:        /mnt/large_writecache_removal


[root@hayes-01 ~]# lvs
  LV                       VG                Attr       LSize Pool        Origin                            Data%  Meta%  Move Log Cpy%Sync Convert
  large_writecache_removal writecache_sanity Cwi-aoC--- 2.00g [pool_cvol] [large_writecache_removal_wcorig] 38.70                                  

# split the cache during the write and cancel it half way through
[root@hayes-01 ~]# lvconvert --splitcache writecache_sanity/large_writecache_removal
  Detaching writecache setting cleaner.
  Detaching writecache cleaning 932457 blocks
  This command can be cancelled and rerun to complete writecache detach.
^C

[root@hayes-01 ~]# lvs -a -o +devices
  LV                                VG                Attr       LSize Pool        Origin                            Data%  Meta%  Move Log Cpy%Sync Convert Devices                           
  large_writecache_removal          writecache_sanity Cwi-aoC--- 2.00g [pool_cvol] [large_writecache_removal_wcorig] 0.01                                    large_writecache_removal_wcorig(0)
  [large_writecache_removal_wcorig] writecache_sanity owi-aoC--- 2.00g                                                                                       /dev/sdb(0)                       
  [pool_cvol]                       writecache_sanity Cwi-aoC--- 1.00g                                                                                       /dev/sdc(0)                       

# Restart the splitcache a second time and let it and the i/o finish
[root@hayes-01 ~]# lvconvert --splitcache writecache_sanity/large_writecache_removal
  Detaching writecache setting cleaner.
  Detaching writecache finished cleaning.
  Logical volume writecache_sanity/large_writecache_removal writecache has been detached.

[root@hayes-01 ~]# lvs -a -o +devices
  LV                       VG                Attr       LSize Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices    
  large_writecache_removal writecache_sanity -wi-ao---- 2.00g                                                     /dev/sdb(0)
  pool                     writecache_sanity -wi------- 1.00g                                                     /dev/sdc(0)

# verify the data on the single origin volume 
[root@hayes-01 ~]# /usr/tests/sts-rhel8.3/bin/checkit -w /mnt/large_writecache_removal -f /tmp/checkit_origin_1 -v
checkit starting with:
VERIFY
Verify XIOR Stream: /tmp/checkit_origin_1
Working dir:        /mnt/large_writecache_removal

FYI - this verification process doesn't work with striped wc origin volumes (See bug 1921214).

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (lvm2 bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2021:1659