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id = 1366
title = "Data inconsistency on LVM logical volume mounted as partition on ubuntu guest, when the written file's size is equal or greater than 27G."
state = "closed"
created_at = "2022-12-15T01:22:29.483Z"
closed_at = "2023-01-04T11:13:40.834Z"
labels = ["Storage"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/1366"
host-os = "Ubuntu 20.04.1"
host-arch = "x86"
qemu-version = "5.0.0"
guest-os = "Ubuntu 22.04"
guest-arch = "x86"
description = """On the guest, writing a 27Gib file or larger result in inconsistent file checksum upon subsequent read."""
reproduce = """**On the host**
0. Create a LVM logical volume on a Linux RAID 1 (with 1 disk only)
```
--- Logical volume ---
LV Path /dev/davidahw2-vg4/lv0
LV Name lv0
VG Name davidahw2-vg4
LV UUID 5FbDcl-eSDe-7cXL-22tj-Lg6O-79AL-4Gq7gx
LV Write Access read/write
LV Creation host, time davida-hw2, 2021-12-06 16:45:00 +0800
LV Status available
# open 1
LV Size <7.28 TiB
Current LE 1907688
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:4
--- Segments ---
Logical extents 0 to 1907687:
Type linear
Physical volume /dev/md4
Physical extents 0 to 1907687
```
1. Format the logical volume as ext4
```
mkfs -t ext4 /dev/davidahw2-vg4/lv0
```
2. Create a libvirt x86 64bits Ubuntu 22.04 machine mounting a LVM logical volume
```
<controller type='scsi' index='1' model='virtio-scsi'><driver queues='8' iothread='2'/></controller>
<disk type='block' device='disk'>
<driver name='qemu' type='raw'/>
<source dev='/dev/davidahw2-vg4/lv0'/>
<target dev='sdd' bus='scsi'/>
<blockio logical_block_size='512' physical_block_size='4096'/>
<address type='drive' controller='1' bus='0' target='1' unit='0'/>
</disk>
```
**On the guest**
3. Mount libvirt/qemu provided block device /dev/sdd as ext4 partition
```
mount /dev/sdd /mnt/test
```
4. Write **27G file** or larger **on the guest** causing the **2nd checksum to be different**
```
sync; head -c 27G </dev/urandom >myfile; sha256sum myfile; sha256sum myfile
8d3b4b263961d2c510390f99879be89b4b9134dc588139ede75573be1590115b myfile
a8e886b3c39d9b4721e582c5e2ca25c76ff6561750ac6dc7aa7e70404661d1cf myfile <== ERROR: Inconsistent checksum
```
5. Write **26G file** or larger **on the guest** and **both checksum are the same**
```
sync; head -c 26G </dev/urandom >myfile; sha256sum myfile; sha256sum myfile
598ac5da9b5bfa14d0ee664ae2590e09da772cba64cbc83ec049a656223c9401 myfile
598ac5da9b5bfa14d0ee664ae2590e09da772cba64cbc83ec049a656223c9401 myfile <== CORRECT: Consistent checksum
```
**Important**:
- With the VM shutdown, the same commands on the same mounted ext4 partition **on the host** has consistent checksum every time for file sizes from 20G to 40G.
- The disk has no sign of failure (no badblocks reported to the filesystem, MD raid reports a healthy raid setup, smart reports on error)"""
additional = """"""
|