SAN Storage

LEARNING 3PAR – PART 1 – CHUNKLETS, LOGICAL DISK, CPGS, AND VIRTUAL VOLUMES

Posted by AMITESHJSK | Learning 3PAR     

First of all we have to know that what SAN storage is. So I’m telling here in easy words:-

What is SAN storage?

A Storage Area Network (SAN) is a specialized, high-speed network that provides block-level network access to storage. SANs are typically composed of hosts, switches, storage elements, and storage devices that are interconnected using a variety of technologies, topologies, and protocols. SANs may also span multiple sites.

A SAN presents storage devices to a host such that the storage appears to be locally attached. This simplified presentation of storage to a host is accomplished through the use of different types of virtualization.

Why we use it?

SANs are often used to:

• Improve application availability (e.g., multiple data paths)
• Enhance application performance (e.g., off-load storage functions, segregate networks, etc.)
• Increase storage utilization and effectiveness (e.g., consolidate storage resources, provide tiered storage, etc.), and improve data protection and security.
• SANs also typically play an important role in an organization's Business Continuity Management (BCM) activities.

SANs are commonly based on Fibre Channel (FC) technology that utilizes the Fibre Channel Protocol (FCP) for open systems and proprietary variants for mainframes. In addition, the use of Fibre Channel over Ethernet (FCoE) makes it possible to move FC traffic across existing high speed Ethernet infrastructures and converge storage and IP protocols onto a single cable. Other technologies like Internet Small Computing System Interface (iSCSI), commonly used in small and medium sized organizations as a less expensive alternative to FC, and InfiniBand, commonly used in high performance computing environments, can also be used. In addition, it is possible to use gateways to move data between different SAN technologies.

Now Introduction to HPE 3PAR Device-

5 Layers to the hosts

As with any array the path that data takes to get from our hosts to its’ final destination on disk is a complex one – but thankfully we don’t have to worry about all of the bumps in the road along the way.  That said it’s always nice to understand the road as best we can in order to determine how best practices and configuration changes will apply to our environment.  With the 3PAR that path contains 5 essential layers; Virtual Volumes, Common Provisioning Groups, Logical Disks, Chunklets, and Physical Disks.

 Figure: - 1. HPE 3PAR StoreServ system data layers

We can somewhat see by the diagram the relationship between each layer but before taking a holistic view let’s first discuss each layer…

Physical Disks

This is an easy one right?  A physical disk is just that, a physical disk located inside of your 3PAR array, encompassing all types of disk within the array.

Chunklets

The first thing a 3PAR does when it is discovering its’ storage is break down all of the capacity on your physical disks into chunklets.  Each chunklet is 1GB in size and occupies contiguous space on a physical disk.  Chunklets are local to that physical disk only and cannot span to others.

Logical Disks

Logical disks are essentially a grouping of chunklets which are arranged as rows of like RAID sets. LD’s will ensure that each chunklet which resides in a RAID set is physically located on different physical disks.  We don’t directly create LD’s on the 3PAR – they are generated during the creation of a CPG (explained next), more-so, when a Virtual Volume is created on a CPG.   All of the metadata however, RAID type, allocation, growth of an LD is defined when creating the CPG itself.

Common Provisioning Groups (CPG)

A CPG is simply a pool of Logical Disks that provide the means for a Virtual Volume (explained next) to consume space.  When we deploy a CPG we do not actually use any of the space in our pooled logical disks until a virtual volume is created – meaning a 2TB CPG with no virtual volumes consumes no space at all.  We can think of a CPG similar to that of an EVA’s disk group, but feeding on logical disks instead of physical disks.

Virtual Volumes (VVs)

No, these aren’t the VVOLs you’re looking for – this is simply a terminology that 3PAR uses to define the LUNs that are presented to the hosts – they are not the VVOLs which we have all seen come supported in vSphere 6.  Either way a Virtual Volume is a LUN that draws its capacity from a CPG – one CPG can provide space to many virtual volumes.  A virtual volume is the LUN that is exported out to your ESXi hosts, and eventually hosts datastores.  Just like most arrays Virtual Volumes can be provisioned either thick or thin – with a thin provisioned Virtual Volume only instructing its associated CPG to draw space from the logical disks as space is needed.  CPGs have the ability to create logical disks as needed to handle the increased demand for capacity up until the user-defined size limit of the CPG is reached.

So working backwards we can come to somewhat of the following

·         A datastore is located on a Virtual Volume

·         A Virtual Volume draws its’ space from a Common Provisioning Group (CPG).

·         A Common Provisioning Group is any given number of Logical Disks joined together to form some sort of contiguous space.

·         A Logical Disk is simply a collection of chunklets which are joined together in rows in order to produce a certain RAID set (0,1,5 etc).

·         A Chunklet is a 1GB piece (chunk) of any given physical disk within the array.  It’s also a very funny word.

·         A physical disk is…well, a physical disk.

Figure: - 2 Configuration of an HPE 3PAR StoreServ Storage system

So there we have it – it being the very basic understanding of some of the terminology within the HP 3PAR.  Certainly we can dive deeper into some of these terms here and we will in later posts – I mean, there are many different types of Chunklets, some reserved, some spare, but we will save those and some other terms such as Adaptive Optimization for another post.