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22 Dell EMC SC Series: Red Hat Enterprise Linux Best Practices | CML1031
3.5 Thin-provisioned volumes
SC Series storage provides the flexibility to create large volumes upfront without consuming much space
thanks to the thin provisioning feature. All SC Series volumes are thin-provisioned by default. No space is
consumed until the applications start writing data to the volumes. When volumes eventually approach full
capacity, administrators can easily and dynamically expand the volumes without affecting the Linux operating
system and applications. Monitor the actual volume space usage in the volume summary and volume
statistics sections in the DSM GUI.
While it is not possible to shrink an SC Series volume size, it is possible to reclaim unused space to reduce
the actual volume space consumption after data/files have been deleted from the volume (see sections 3.8.2
and 3.9.3).
3.6 Multipathing
Multipathing is a software solution implemented at the host-operating-system level. While multipathing is
optional, it provides path redundancy, failover, and performance-enhancing capabilities. Therefore, it is highly
recommended to deploy the solution in a production environment or environments where availability and
performance are critical.
The main benefits of using an MPIO solution include the following:
• Increase application availability by providing automatic path failover and failback.
• Enhance application I/O performance by providing automatic load balancing and capabilities for
multiple parallel I/O paths.
• Ease administration by providing persistent user-friendly names for the storage devices across cluster
nodes.
3.6.1 Presenting SC Series volumes with multiple access paths
To allow multiple access paths to the SC Series storage system, the following requirements should be met.
• Have at least two FC/iSCSI or SAS HBAs on the Linux system to provide path redundancy.
• Use multiple switches to provide switch redundancy.
• Use virtual ports and create two fault domains on the SC Series storage system.
• Configure proper FC zoning or a network VLAN (see the SC Series Owner’s Manual on
http://support.dell.com).
• Ensure all paths to the same volume use the same transport protocol and have similar performance
characteristics. While it is possible to mix the FC and iSCSI access paths to the same volume, it is
not recommended due to the difference in performance.
• If a Linux system provides both FC and iSCSI access, create one server object per transport protocol
in DSM GUI to represent the Linux system. Do not include both FC and iSCSI access points in the
same server object. For example, a server object with two FC access points to HostA and another
server object with two iSCSI access points to the same HostA (see Figure 2)
• Map an SC Series volume to either an FC or iSCSI server object. This way, a Linux system can
access both FC volumes and iSCSI volumes on the same SC Series storage system.