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Bug 1668747

Summary:	vdostats displays a large number for volumes started in read-only mode
Product:	Red Hat Enterprise Linux 8	Reporter:	Bryan Gurney <bgurney>
Component:	vdo	Assignee:	sclafani
Status:	CLOSED ERRATA	QA Contact:	vdo-qe
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	8.1	CC:	awalsh, msakai, rhandlin
Target Milestone:	rc	Flags:	pm-rhel: mirror+
Target Release:	8.0
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	6.2.1.6	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2019-11-05 22:12:24 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	1682564
Bug Blocks:

Description Bryan Gurney 2019-01-23 13:50:42 UTC

Description of problem:

In VDO 6.1.1 in RHEL 7.6, a read-only VDO volume displayed a "data blocks used" statistics of "N/A", which would result in a "vdostats --verbose" display resembling the following:

vdo : 
  version                             : 28
  release version                     : 131337
  data blocks used                    : N/A
  overhead blocks used                : 940924
  logical blocks used                 : 0
  physical blocks                     : 217849600
  logical blocks                      : 104857600
  1K-blocks                           : 871398400
  1K-blocks used                      : N/A
  1K-blocks available                 : N/A
  used percent                        : N/A
  saving percent                      : N/A

(This is with the value in /sys/kvdo/vdo1/statistics/data_blocks_used being "0".)

In VDO 6.2.0 on RHEL 8, a read-only VDO volume seems to display the value of "data blocks used", even if the volume is read-only.

vdo1 : 
  version                             : 30
  release version                     : 133524
  data blocks used                    : 0
  overhead blocks used                : 1065312
  logical blocks used                 : 0
  physical blocks                     : 26214144
  logical blocks                      : 104857600
  1K-blocks                           : 104856576
  1K-blocks used                      : 4261248
  1K-blocks available                 : 100595328
  used percent                        : 4
  saving percent                      : 0
  block map cache size                : 134217728
  write policy                        : sync
  block size                          : 4096
  completed recovery count            : 0
  read-only recovery count            : 0
  operating mode                      : read-only

If the "data blocks used" value is non-zero prior to the read-only event, a very large number may appear.  This is after having executed "mkfs.xfs -K /dev/mapper/vdo1" on the volume, prior to triggering read-only mode:

vdo1 : 
  version                             : 30
  release version                     : 133524
  data blocks used                    : 18446744073709551365
  overhead blocks used                : 1065563
  logical blocks used                 : 51291
  physical blocks                     : 26214144
  logical blocks                      : 104857600
  1K-blocks                           : 104856576
  1K-blocks used                      : 73786976294842467712
  1K-blocks available                 : -73786976294737611136
  used percent                        : 70369431379146
  saving percent                      : 0
  block map cache size                : 134217728
  write policy                        : sync
  block size                          : 4096
  completed recovery count            : 0
  read-only recovery count            : 0
  operating mode                      : read-only

(Note that in both RHEL 7.6 and RHEL 8.0, /sys/kvdo/vdo1/statistics/data_blocks_used says 18446744073709551365.  However, the vdostats program from vdo-6.1.1.125 displays "N/A" for the "data blocks used" field, and the other calculated fields.)

Version-Release number of selected component (if applicable):
kernel-4.18.0-63.el8.x86_64
kmod-kvdo-6.2.0.293-44.el8.x86_64
vdo-6.2.0.293-10.el8.x86_64


How reproducible:


Steps to Reproduce:
1. vdo create --name=vdo1 --device=/dev/nvme0n1p1 --vdoLogicalSize=400G
2. vdostats --verbose vdo1 | grep data\ blocks\ used
3. mkfs.xfs -K /dev/mapper/vdo1
4. vdostats --verbose vdo1 | grep data\ blocks\ used
5. vdo stop --name=vdo1
6. vdoreadonly /dev/nvme0n1p1
7. vdo start --name=vdo1
8. vdostats --verbose vdo1 | grep data\ blocks\ used


Actual results:
The "vdostats --verbose" command displays a very large number for VDO volumes that previously had a nonzero "data blocks used" statistic.

Expected results:
The "vdostats --verbose" command displays "N/A" for "data blocks used".

Additional info:

RHEL 7 / VDO 6.1.1 comparison point versions:

kernel-3.10.0-957.1.3.el7.x86_64
vdo-6.1.1.125-3.el7.x86_64
kmod-kvdo-6.1.1.125-5.el7.x86_64

Comment 1 Bryan Gurney 2019-01-23 14:12:29 UTC

How reproducible: seems to be 100%, as long as at least one data block is written.  (I've only had enough time to run "mkfs.xfs -K" on the VDO volume so far).

Here's what the non-verbose vdostats output looks like (on the RHEL 8 test system):

# vdostats
Device               1K-blocks      Used Available Use% Space saving%
/dev/mapper/vdo1     104856576 73786976294842467712 -73786976294737611136 70369431379146%            0%

# dmsetup status vdo1
0 838860800 vdo /dev/nvme0n1p1 read-only - online online 1065312 26214144

Comment 6 Jakub Krysl 2019-07-25 12:12:18 UTC

kmod-kvdo-6.2.1.102-53.el8.x86_64
kernel-4.18.0-107.el8.x86_64
vdo-6.2.1.102-11.el8.x86_64

# vdo create --name=vdo1 --device=/dev/sda --vdoLogicalSize=400G
Creating VDO vdo1
Starting VDO vdo1
Starting compression on VDO vdo1
VDO instance 0 volume is ready at /dev/mapper/vdo1

# vdostats --verbose vdo1 | grep data\ blocks\ used
  data blocks used                    : 0

# mkfs.xfs -K /dev/mapper/vdo1
meta-data=/dev/mapper/vdo1       isize=512    agcount=4, agsize=26214400 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=1        finobt=1, sparse=1, rmapbt=0
         =                       reflink=1
data     =                       bsize=4096   blocks=104857600, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0, ftype=1
log      =internal log           bsize=4096   blocks=51200, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
# vdostats --verbose vdo1 | grep data\ blocks\ used
  data blocks used                    : 6

# vdo stop --name vdo1
Stopping VDO vdo1

# vdoreadonly /dev/sda

# vdo start --name vdo1
Starting VDO vdo1
Starting compression on VDO vdo1
VDO instance 1 volume is ready at /dev/mapper/vdo1

# vdostats --verbose vdo1 | grep data\ blocks\ used
  data blocks used                    : N/A

Comment 9 errata-xmlrpc 2019-11-05 22:12:24 UTC

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, 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-2019:3548