One of the brightest stars in the storage firmament
today isthin
provisioning. Offering immediate benefits for
both IT administrators and CFOs, true thin provisioning can be
great news in the datacentre. So how can you identify the "real
thing"?
Large or small allocation unit?
How much physical capacity is consumed when a write is
received?
As data is written, different implementations of thin
provisioning will consume varying amounts of capacity. Where the
unit of consumption is much greater than the size of the write, the
efficiencies are diminished. When scores of megabytes are dedicated
on even the smallest of writes, the simple creation of a file
system on a thin provisioned volume can fill the volume,
eliminating any value of thin provisioning before the first file is
even written.
Conversely, fine-grained allocation, where capacity is dedicated
in kilobytes, maximises capacity savings and thin provisioning can
easily be applied broadly to many host operating systems, file
systems and applications.
Reserved or reservationless?
Is physical capacity pre-configured for and reserved upfront
into specific thin provisioning pools?
With "reserved" implementations, physical capacity is
pre-configured and committed upfront into specific thin
provisioning pools, which is a tremendous waste.
With "reservationless" implementations, capacity is drawn and
configured in fine increments from a single pool with no
pre-dedication.
Manual or autonomic?
Do administrators have to manually configure storage and Raid
groups into pools to keep them replenished?
In traditional storage environments, capacity is dramatically
over-provisioned to avoid the disadvantages of manual
re-provisioning. Manual thin provisioning retains much of the
original complexity, where decisions cannot be easily undone, and
pool provisioning may be quite conservative, severely mitigating
the benefits of thin provisioning.
With "autonomic" thin provisioning, capacity is dedicated and
configured without human intervention and just-in-time, eliminating
user time and effort and any compensating inefficiencies.
Dual controller or massively scalable?
Can you aggregate lots of distinct workloads? Do you have room
to backfill virtual capacity with physical capacity and performance
upgrades?
Thin provisioning is about making capacity promises that may
have to be kept in the future. Hence array scalability is of utmost
concern. Dual controller architectures are disadvantaged in this
respect, but scalable systems are ideal for thin provisioning since
they are already architected for storage consolidation and
growth.
Bolt-on or built-in
Is thin provisioning an afterthought, forcing trade-offs between
one benefit and another, or is it fully integrated with all other
functionality?
Sometimes thin provisioning is added to a pre-existing hardware
and software architecture, leading to unhappy trade-offs such as
diminished performance, loss of other functionality and inadequate
monitoring. Meanwhile, hardware and software architectures built to
support thin provisioning offer full integration for safe,
confident operation.
Thin provisioning can be a tremendous boon for most
organisations. But the benefits will depend on the technology
features, which can vary dramatically from supplier to supplier.
The checklist above can serve as a reliable starting point.
● 3PAR's David Scott will be speaking on "Thin Provisioning:
Sparking a Green Storage Revolution" in his seminar at Storage Expo
2007