[linux-lvm] Lvm think provisioning query

[Bhasker C V <bhasker@unixindia.com>]

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Hi,

 I am starting with investigating about the lvm thin provisioning
 (repeat post from
https://lists.debian.org/debian-user/2016/04/msg00852.html )
 (apologies for html mail)

 I have done the following

1.Create a PV
vdb    252:16   0   10G  0 disk
├─vdb1 252:17   0  100M  0 part
└─vdb2 252:18   0  9.9G  0 part
root@vmm-deb:~# pvcreate /dev/vdb1
  Physical volume "/dev/vdb1" successfully created.
root@vmm-deb:~# pvs
  PV         VG   Fmt  Attr PSize   PFree
  /dev/vdb1       lvm2 ---  100.00m 100.00m

2. create a VG
root@vmm-deb:~# vgcreate virtp /dev/vdb1
  Volume group "virtp" successfully created
root@vmm-deb:~# vgs
  VG    #PV #LV #SN Attr   VSize  VFree
  virtp   1   0   0 wz--n- 96.00m 96.00m

3. create a lv pool  and a over-provisioned volume inside it
root@vmm-deb:~# lvcreate -n virtpool -T virtp/virtpool -L40M
  Logical volume "virtpool" created.
root@vmm-deb:~# lvs
  LV       VG    Attr       LSize  Pool Origin Data%  Meta%  Move Log
Cpy%Sync Convert
  virtpool virtp twi-a-tz-- 40.00m             0.00   0.88

root@vmm-deb:~# lvcreate  -V1G -T virtp/virtpool -n vol01
  WARNING: Sum of all thin volume sizes (1.00 GiB) exceeds the size of thin
pool virtp/virtpool and the size of whole volume group (96.00 MiB)!
  For thin pool auto extension activation/thin_pool_autoextend_threshold
should be below 100.
  Logical volume "vol01" created.
root@vmm-deb:~# lvs
  LV       VG    Attr       LSize  Pool     Origin Data%  Meta%  Move Log
Cpy%Sync Convert
  virtpool virtp twi-aotz-- 40.00m                 0.00   0.98

  vol01    virtp Vwi-a-tz--  1.00g virtpool        0.00


---------- Now the operations
# dd if=/dev/urandom of=./fil status=progress
90532864 bytes (91 MB, 86 MiB) copied, 6.00005 s, 15.1 MB/s^C
188706+0 records in
188705+0 records out
96616960 bytes (97 MB, 92 MiB) copied, 6.42704 s, 15.0 MB/s

# df -h .
Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/virtp-vol01  976M   95M  815M  11% /tmp/x
# sync
# cd ..
root@vmm-deb:/tmp# umount x
root@vmm-deb:/tmp# fsck.ext4 -f -C0  /dev/virtp/vol01
e2fsck 1.43-WIP (15-Mar-2016)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure

Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/virtp/vol01: 12/65536 files (8.3% non-contiguous), 36544/262144 blocks


<mount>
# du -hs fil
93M    fil

# dd if=./fil of=/dev/null status=progress
188705+0 records in
188705+0 records out
96616960 bytes (97 MB, 92 MiB) copied, 0.149194 s, 648 MB/s


# vgs
  VG    #PV #LV #SN Attr   VSize  VFree
  virtp   1   2   0 wz--n- 96.00m 48.00m

Definetly the file is occupying 90+MB.

What i expect is that the pool is 40M and the file must NOT exceed 40M.
Where does the file get 93M space ?
I know the VG is 96M but the pool created was max 40M (also VG still says
48M free). Is the file exceeding the boundaries ?
or am I doing anything wrong ?

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