This document provides a detailed overview of the VxVM device naming and reporting enhancements implemented in Storage Foundation 5.0 MP3 for Unix and Linux.
Improving Efficiency with Device Naming Consistency
As configurations in the datacenter scale up and more SAN devices and nodes have to be managed, there is a greater need for consistency and predictability in device naming. Higher consistency streamlines operations, facilitates troubleshooting and reduces the risk for configuration errors.
Storage Foundation supports two device naming schemes – Operating System Native (OSN) names and Enclosure Based Names (EBN). The enclosure based names comprise of two parts; the enclosure name prefix and the device index suffix. For example, the EBN EMC0_19 for a SAN device presented from an EMC enclosure comprises two parts:
- The enclosure name prefix EMC0 that identifies the enclosure model (EMC) and assigns it an enclosure index (00) in order to differentiate between multiple enclosures of the same type.
- The device index suffix 19 that uniquely identifies the device within that enclosure.
Device name consistency requires the enclosure name prefix and device index suffix to be the same across all hosts in the cluster. Enclosure name consistency usually is not a problem because hosts seldom are connected to multiple enclosures of the same type, and when they are, the number of enclosures is small enough that consistency can be ensured through manual configurations. Device index consistency on the other hand requires an automated approach. As depicted in the figure above, Storage Foundation 5 .0 MP3 enables consistency of t he device names through enhancements to enclosure based names (EBN).
SF 5.0 MP3 enables naming consistency in the following manner:
- Storage Foundation goes deeper into storage arrays and discovers the short array volume identifiers (AVID) that are used for identification and management of array volumes on the storage management console. The device index suffix of an EBN is set to match the discovered AVID. This ensures consistency of the name across all hosts connected to the same SAN device. It also ensures consistency of the name between hosts and storage, facilitating communication between system and storage administrators.
AVIDs are usually hardware specific. On an EMC DMX for example, the AVID matches a device’s LUN Ids viewable from the Solution Enabler SYMCLI, while on HDS or HP XP storage, the AVID corresponds to a device’s CU:LDEV.
- When Storage Foundation does not have access to a device’s AVID, it retrieves another unique LUN identifier called Lun serial number. It sorts the devices based on the Lun Serial Number (LSN) and uses the index to create the suffix for the device name. All hosts see the same set of devices, so all hosts will have the same sorted list, leading to consistent device indices across the cluster.
- Finally, Storage Foundation supports a scalable framework allowing users to fully customize the device names on a host by applying a ‘device naming file’ that associates custom names with cabinet and lun serial numbers.
Streamlining Operations through Enhanced Storage Visibility
A related challenge for system administrators managing large numbers of SAN devices on hosts is getting enough information on the storage to perform day to day operations efficiently and without errors. Storage Foundation 5.0 MP3 brings a number of enhancements on that front with new commands (such as vxdmpadm list dmpnode) that provide consolidated reports of all information related to a device, as well as enhanced CLI for most DMP configurations. To further facilitate getting acquainted with the new functionality, all online help messages for vxdmpadm and vxddladm have been revamped. When configuring volumes on a Storage Foundation host, system administrators typically have to consider characteristics of the underlying storage. For example, some applications need to be configured on replicated storage, while others need to be on hardware mirrors. To facilitate such configurations, Storage Foundation 5.0 MP3 discovers and reports device attributes such as BCV, SRDF, PVOL, SVOL, Thin, etc. in the output of vxdisk list.
For more technical details on those enhancements, including screenshots and typical use cases, download the attached paper.