Configure a storage pool's caching properties

Prerequisites

Before you can configure a storage pool's cache, pool caching must be disabled on your cluster. Refer to the Disable pool caching page for more details.

Configure a storage pool's cache

1. Enter pool maintenance mode:

   pxctl service pool maintenance --enter

   Pool transition operation will restart PX.
   Are you sure you want to proceed ? (Y/N): Y
   Pool transition request submitted.

2. Enter the pxctl service pool cache configure command, specifying:

• The --mode option with the caching <mode>

• The --blocksize option with the <block_size> the cache uses

• The --policy option with the caching <policy>

• The --tunables option with the comma delimited <tunable> parameters

• The <pool_id> of the pool you're updating

  pxctl service pool cache configure \
  --mode [ writeback | writethrough] \
  --blocksize [ cache block size, "auto"]\
  --policy [ smq | mq \]\
  --tunables [ one or more comma separated parameters from below ]\
  <pool ID>

  The following example configures a pool with an ID of 0:

  pxctl service pool cache configure --mode writeback --blocksize "auto" --policy smq --tunables migration_threshold=2048000 0

  Cache parameters updated, check using 'pxctl service pool cache status 0'

  The migration_threshold parameter represents the number of 512-byte sectors allowed at any time to migrate data from either cache to origin or the other way round. Portworx automatically computes the default value of this parameter based on the assigned cache capacity for a given pool. If it's 1MB, then the default migration bandwidth is set to 100 times the cache block size at 100MB. This translates to 204800 512 byte sectors.

  note

  Note: Use caution when running this command. If you misconfigure the tunable arguments, Portworx may behave unexpectedly or perform poorly.

3. Run the pxctl service pool cache status command with the id of the pool as a parameter to check if the new settings are applied:

   pxctl service pool cache status 0

   PX Cache Configuration and Status:
   Pool ID:  0
     Enabled:  false
     Members:  [/dev/sdc]
     TotalBlocks: 0
     UsedBlocks: 0
     DirtyBlocks: 0
     ReadHits: 0
     ReadMisses: 0
     WriteHits: 0
     WriteMisses: 0
     BlockSize: 1048576
     Mode: writeback
     Policy: smq
     Tunables: migration_threshold=2048000

4. Exit pool maintenance mode:

   pxctl service pool maintenance --exit

   Pool transition operation will restart PX.
   Are you sure you want to proceed ? (Y/N): Y
   Pool transition request submitted.