From the Lenovo webinar series: some ONTAP technologies in DM series storage systems

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Although the usual offline events have many undeniable advantages, online seminars and lectures are quite adequate as a means of establishing communication between product experts of vendors and distributors, on the one hand, and IT specialists of partners and customers, on the other. Lenovo offers access to many of its previous webinars on modern data center technologies through its dedicated site

The webinars are designed for a wide audience of IT professionals, both for those who are not yet familiar with Lenovo’s data center offerings, and for existing customers and partners of the company. CRN / RE readers will certainly be interested in the presentation of Anton Kittson, Storage Product Manager, presented in this series, in which he reviewed some ONTAP technologies in Lenovo DM series devices. Storage systems have been radically transformed in recent years; traditional tools for accumulating and analyzing data are no longer able to cope with the urgent tasks of our time. More powerful hardware and software and standardized, centralized data management are needed. These are the tools that Lenovo offers in its DM series storage systems.


Hardware architecture

Lenovo’s lineup includes two series of storage systems, and one of them, DM, is based on ONTAP technologies from Lenovo’s strategic partner, NetApp. The essence of the ONTAP approach is to separate the physical and logical layers of data storage, providing the end user and applications with convenient and easy access to them, while providing administrators with the ability to expand the available storage volumes without the need to suspend the storage system and even without any noticeable impact. on its performance. In other words, ONTAP for storage systems seems to be a kind of analogue of server virtualization, but with a pronounced emphasis on the reliability of data storage and their guaranteed availability.

Rice. 1. Lenovo storage controller DM series

The internal architecture of the ONTAP-based system differs from other dual-controller storage systems available on the market. Storage systems Lenovo DM series are built on a cluster principle, starting from a separate node. From an ONTAP storage perspective, these nodes form one large cluster. Within one cluster, you can currently combine up to 24 nodes, if this cluster is a file one. If you need to work with storage systems as with a universal cluster, if you need support for various protocols, block access, iSCSI, FC, etc., then in this mode the cluster can be expanded to 12 nodes.

In the controller itself, in addition to the necessary components such as a processor, cache, ports, expansion slots, there is an important element that is a distinctive feature of ONTAP systems – an NVRAM module, non-volatile memory. It is its application that allows you to reliably protect data from all kinds of failures, including loss of power, unavailability or reboot of the controller.

Rice. 2. Schematic diagram of the HA-pair and its implementation in the rack

Two ONTAP-controllers with communication buses between them form the so-called HA-pair (from high availability, “high availability”). In modern storage systems, two controllers are minimally mounted, and the further increase in their number also goes in pairs. Each controller from the HA-pair has direct access not only to “its” drives, but also to disks under the direct control of the second controller from the pair. This principle of HA-pair organization – failover, failover – implies that at any moment, in the event of a failure, the partner node will take control of its neighbor’s disks. Communication between the nodes of the HA-pair is provided by the HA-interconnect bus. In addition, there are also inter-cluster connections based on a network that operates within ONTAP systems.

For service operations – during setup or during maintenance – the controllers can be accessed via their own dedicated IP addresses. In all other cases, access to the data warehouse node is performed exclusively through a single cluster IP. This is how a full-fledged cluster ONTAP system is implemented: through a dedicated network designed to access data, users and applications get access to information on the storage system using various protocols (Ethernet, FC, etc.). The controllers in Lenovo DM are connected to each other through dedicated ports with separate cables that are always included with the storage system: this is the so-called switchless connection scheme. For a storage system with two controllers, this is sufficient. If there are more than two controllers in the system, it is necessary to implement the already switched-scheme, when switches external to the controllers are used to organize an inter-cluster connection.

Rice. 3. Organization of inter-cluster connections by means of external switches (switched)

An important distinguishing feature of the ONTAP system is its design flexibility. Within one cluster, you can combine storage systems of different levels and even different generations. It is inter-cluster connections that allow you to form a single namespace, organize a single addressing and a single control. In particular, within ONTAP systems, excellent collaboration of storage systems of different models, different generations, even with different types of drives, is provided – these can be disk, all-flash, and hybrid models.

Physical and logical layers

ONTAP systems do not use the most common RAID types. The fact is that the recording, which is organized by ONTAP on disks, is performed by the so-called. a single block-level stripe. A single piece of data (stripe) is formed in the cache for all disks in the system, and this portion is written at once to the entire set of drives presented in the configuration. To improve the performance and transparency of this operation, special RAID types were developed.