You can restrict a volume to a subset of a cluster's nodes. By doing this, you can isolate sensitive data or applications, and even use heterogeneous hardware in the cluster for specific workloads.

For example, you can use data placement to keep personally identifiable information on nodes that have encrypted drives, or to keep MapR-DB tables on nodes that have SSDs. You can also isolate work environments for different database users or applications and place MapR-DB tables on specific hardware for better performance or load isolation

Isolation of work environments for different database users or applications lets you set policies, quotas, and access privileges at for specific users and volumes. You can run multiple jobs with different requirements without conflict.

As an example, the diagram below depicts a MapR cluster storing table and file data. The cluster has three separate volumes mounted at directories /user/john, /user/dave, and /project/ads. As shown, each directory contains both file data and table data, grouped together logically. Because each of these directories maps to a different volume, data in each directory can have different policy. For example, /user/john has a disk-usage quota, while /user/dave is on a snapshot schedule. Furthermore, two directories, /user/john and /project/ads are mirrored to locations outside the cluster, providing read-only access to high-traffic data, including the tables in those volumes.

Example: Restricting table storage with quotas and physical topology

This example creates a table with disk usage quota of 100GB restricted to certain data nodes in the cluster. First, we create a volume named project-tables-vol, specifying the quota and restricting storage to nodes in the /data/rack1 topology, and mounting it in the local namespace. Next, we use the HBase shell to create a new table named datastore, specifying a path inside the project-tables-vol volume.
$ pwd 

bin   src

$ maprcli volume create -name project-tables-vol -path /user/project/tables \
    -quota 100G -topology /data/rack1  

$ ls
bin   src   tables

$ hbase shell
HBase Shell; enter 'help<RETURN>' for list of supported commands.
Type "exit<RETURN>" to leave the HBase Shell
hbase(main):001:0> create '/user/project/tables/datastore', 'colfamily1'
0 row(s) in 0.5180 seconds
hbase(main):002:0> exit

$ ls -l tables
total 1
lrwxr-xr-x 1 mapr mapr 2 Oct 25 15:20 datastore -> mapr::table::2252.32.16498

See Multi-tenancy with MapR for more details.