Enable pool caching

Prerequisites

Before you can enable pool caching, you must have a storage pool with caching configured but currently disabled.

You can use the following commands to check if caching is disabled:

1. Run the pxctl status command the get the id of your pool:

   pxctl status

   Status: PX is operational
   License: Trial (expires in 29 days)
   Node ID: xxxxxxxx-xxxx-xxxx-xxxx-f929bc658862
   	IP: X.X.X.28
   	Local Storage Pool: 1 pool
   	POOL	IO_PRIORITY	RAID_LEVEL	USABLE	USED	STATUS	ZONE	REGION
   	0	HIGH		raid0		128 GiB	8.4 GiB	Online	default	default
   	Local Storage Devices: 2 devices
   	Device	Path		Media Type		Size		Last-Scan
   	0:0	/dev/sdf	STORAGE_MEDIUM_MAGNETIC	128 GiB		22 Sep 19 14:48 UTC
   	total			-			128 GiB
   	Cache Devices:
   	Device	Path		Media Type		Size		Last-Scan
   	0:1	/dev/sdc	STORAGE_MEDIUM_SSD	70 GiB		22 Sep 19 14:48 UTC
   Cluster Summary
   	Cluster ID: doc-cluster-caching-2.2.0
   	Cluster UUID: xxxxxxxx-xxxx-xxxx-xxxx-70019d925a4a
   	Scheduler: none
   	Nodes: 3 node(s) with storage (3 online)
   	IP		ID					SchedulerNodeName	StorageNode	UseCapacity	Status	StorageStatus	Version		Kernel				OS
   	X.X.X.28	xxxxxxxx-xxxx-xxxx-xxxx-f929bc658862	N/A			Yes		8.4 GiB	128 GiB		Online	Up (This node)	2.2.0.0-328a043	4.20.13-1.el7.elrepo.x86_64	CentOS Linux 7 (Core)
   	X.X.X.240	xxxxxxxx-xxxx-xxxx-xxxx-2ae648891072	N/A			Yes		8.4 GiB	128 GiB		Online	Up		2.2.0.0-328a043	4.20.13-1.el7.elrepo.x86_64	CentOS Linux 7 (Core)
   	X.X.X.32	xxxxxxxx-xxxx-xxxx-xxxx-9bf257e9973a	N/A			Yes		8.4 GiB	128 GiB		Online	Up		2.2.0.0-328a043	4.20.13-1.el7.elrepo.x86_64	CentOS Linux 7 (Core)
   Global Storage Pool
   	Total Used    	:  25 GiB
   	Total Capacity	:  384 GiB

2. Run the pxctl service pool cache status command with the id of your storage pool as a parameter:

   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=20480

Enable pool caching

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 enable command, specifying the <pool_id> of the pool you want to disable caching for:

   pxctl service pool cache enable <pool_id>

   The following example enables caching for a pool with an ID of 0:

   pxctl service pool cache enable 0

   Pool 0 attached cache successfully

3. 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.

4. At this point you can run the pxctl service pool cache status command to see if caching is enabled:

   PX Cache Configuration and Status:
   Pool ID:  0
   	Enabled:  true
   	Members:  [/dev/sdc]
   	TotalBlocks: 71660
   	UsedBlocks: 10
   	DirtyBlocks: 6
   	ReadHits: 13
   	ReadMisses: 10
   	WriteHits: 14
   	WriteMisses: 8
   	BlockSize: 1048576
   	Mode: writeback
   	Policy: smq
   	Tunables: migration_threshold=20480