[linux-lvm] Question on lvconvert when using to create Cachepool- Gives no space in Volume group

Lakshmi sendtold at gmail.com
Mon Sep 28 18:11:30 UTC 2015

Hi all,

   I am hoping to get some answers, pointers here as I am stuck with
this for quite sometime and need some suggestions to proceed further.

I am using lvm-cache for my test and My current test setup has,

1x1142GB HDD in Raid0
1x387GB SSD in Raid 0
I have RHEL 7.1 and 3.10.0-229.el7.ppc64.
lvm version that was part of the distro
  LVM version:     2.02.115(2)-RHEL7 (2015-01-28)
  Library version: 1.02.93-RHEL7 (2015-01-28)
  Driver version:  4.29.0

pvscan looks like this.

# pvscan
  PV /dev/sdi1 lvm2 [1.04 TiB]
  PV /dev/sdh1 lvm2 [361.31 GiB]

Steps I followed to create the lvm-cache device

1. Created a partition on entire HDD and a partition on entire SSD
2. Created physical volumes for the above partitions
3. Created Volume Group using these 2 PVs
4. Created LVMS as follows

Create  Origin Device logical Volume (origin_device)
lvcreate -L 1024G -n origin_device cache_VG /dev/sdu1

Create a cache meta data logical Volume  (cache_meta)
lvcreate -L 315M -n Cache_Meta Cache_VG /dev/sdw1
>>> used 1/1000(307G) as mentione din lvm-cache manpage

Create a cache  block data logical Volume  (cache_block)
lvcreate -L 307G -n Cache_Block Cache_VG /dev/sdw1

Create a cache pool logical volume by combining cache block and cache meta
data logical volumes (combining step 5 and 6)
lvconvert --type cache-pool --cachemode writeback --poolmetadata
Cache_VG/Cache_Meta Cache_VG/Cache_Block

ISSUE: And I get

  WARNING: Maximum supported pool metadata size is 16.00 GiB.
  WARNING: Converting logical volume Cache_VG/Cache_Meta and
Cache_VG/Cache_Block to pool's data and metadata volumes.
Do you really want to convert Cache_VG/Cache_Meta and Cache_VG/Cache_Block?
[y/n]: y
  Volume group "Cache_VG" has insufficient free space (24077 extents): 78592

Can someone tell me why it complains that it doesnt have enough space,
since the LVMS are already carved from the Volume group and all it does is
convert to a cachepool? I am not aware of the intrenal details of converting
a cache pool, but if somebody could tell me the reason or how i can fix this
, it would be very helpful.

This is my "vgdisplay" output
  --- Volume group ---
  VG Name               Cache_VG
  System ID
  Format                lvm2
  Metadata Areas        2
  Metadata Sequence No  4
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                3
  Open LV               0
  Max PV                0
  Cur PV                2
  Act PV                2
  VG Size               1.39 TiB
  PE Size               4.00 MiB
  Total PE              364892
  Alloc PE / Size       340815 / 1.30 TiB
  Free  PE / Size       24077 / 94.05 GiB

# pvdisplay /dev/sdh1
  --- Physical volume ---
  PV Name               /dev/sdh1
  VG Name               Cache_307GB_VG
  PV Size               361.31 GiB / not usable 3.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              92495
  Free PE               13824
  Allocated PE          78671

# pvdisplay /dev/sdi1
  --- Physical volume ---
  PV Name               /dev/sdi1
  VG Name               Cache_307GB_VG
  PV Size               1.04 TiB / not usable 3.00 MiB
  Allocatable           yes
  PE Size               4.00 MiB
  Total PE              272397
  Free PE               10253
  Allocated PE          262144

Any suggestions , pointers will be really helpful as I am stuck with this
for sometime and I have not been able to proceed.


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