Docker LVM Metadata Calibration

Question

Docker LVM Metadata Calibration

I use the thin LVM pool for storing dockers (dm.thinpooldev), and so far I have run out of metadata space. It’s easy to fight, as I can just recreate a thin pool with great metadata, but I just know (and probably guess) how much this can be done.

Does anyone have any suggestions regarding the relative size of metadata for Docker? It seems that the default values in lvcreate are not enough:

- poolmetadatasize MetadataVolumeSize [bBsSkKmMgG] Sets the size of the logical pool metadata volume. Supported values range between 2MiB and 16GiB for a thin pool, and up to 16GiB for a cache pool. The minimum value is calculated from the size of the pool data. The default value for the thin pool (Pool_LV_size / Pool_LV_chunk_size * 64b). The default unit is megabytes.

The main commands that I use:

DISK=/dev/xvdf
VG=docker_vg
LV=docker_pool
pvcreate $DISK
vgcreate $VG $DISK
lvcreate -l 100%FREE --thinpool $LV $VG

Or replace custom metadata size

lvcreate -l 100%FREE --poolmetadatasize 200M --thinpool $LV $VG

[EDIT] Well, no answer, so now I'm going with 1%. This has worked for us so far, although it is probably still too prepared.

  DISK=/dev/xvdf
  VG=docker_vg
  LV=docker_pool
  DOCKER_POOL_METADATA_PERCENTAGE=1

  DISK_SIZE=$(blockdev --getsize64 ${DISK})
  META_DATA_SIZE=$(echo "scale=0;${DISK_SIZE}*${DOCKER_POOL_METADATA_PERCENTAGE}/100" | bc)
  pvcreate ${DISK}
  vgcreate ${DOCKER_VG} ${DISK}
  # This metadata sizing is in k because bytes doesn't seem to translate properly
  lvcreate -l 100%FREE --poolmetadatasize $((${META_DATA_SIZE}/1024))k --thinpool ${DOCKER_POOL} ${DOCKER_VG}