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.
