This is the fifth of eight in a series titled 8 Must Haves for the IT Director

Number 5 – Space-Efficient Snapshots

The hidden cost of snapshot space hogs

Using snapshots to protect array data is nothing new. What is new is how the aging (or tiered progression) algorithms associated with primary data can also be applied to snapshot data. There are 2 parts to snapshot efficiency; 1) minimizing the amount needed initially and 2) placing the older snapshots on lower tiered groups of disks.

Some storage architectures implement snapshots using large chunks, or pages, of data. These larger block approaches tend to overuse snapshot space by preserving data at a minimum of 15K chunks. Imagine a 15K snapshot for a single byte change. Compellent snapshots can be configured from 512 Byte blocks to 4K, drastically reducing the per change overhead.

Snapshot migration reduces costs

The second snapshot efficiency gained by the Compellent architecture is that, similar to primary data, snapshot data can also be progressively moved to lower speed, lower cost media as it ages. Snapshots for yesterday are generally more likely to be needed than snapshots from a previous month, especially for high-IO applications. Thus, it makes sense that the most recent snapshots are readily available on the fastest tier groups; a process handled automatically by Compellent.

Since Replays are so space efficient, recovery can take as few as 10 seconds and volumes can be
mapped to any server without disruption. To simplify the process, administrators set up Replay
schedules using an intuitive point-and-click interface. Replays can also be used to test new applications
and service packs on actual data without risk, efficiently support boot-from-SAN operations and
virtually eliminate backup windows on production systems.


Next up in our 8 Must Have series is #6, Thin Replication.

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Having dealt with capacity based licensing during most of my career, I was pleasantly surprised that Compellent puts a ceiling on it’s software costs based on the number of drives. Although a Compellent SC040 can scale from 6 to at least 1008 disk drives, the licensing cut off point is 96 drives.

To avoid charging customers for unneeded software, Compellent licenses the following:

1. Data Progression (Block based Automated Tiered Storage) – ILM
2. Data Instant Replay (Snap Shot)
3. Dynamic Capacity (Thin Provisioning) (Prerequisite)
4. Remote Instant Replay (Replication)
5. Replay Manager (Application Aware Snaps)
6. Fast Track (Tiering on the disk for higher performance)
7. Storage Center Core (prerequisite)

You could have all these features or some of them depending on what you’re trying to achieve.

A Base license = 16 active drives.

Expansion licenses are based on 8 drive increments to a maximum of 10 sets or a total of 96 drives including Base license.

So, once you hit the 96 drive number, you don’t buy anymore SW, just hardware and probably just 7K drives. Compellent say 7K drives make up 81% of their disk upgrades.

One caveat is that although you are not “charged” for software beyond 96 drives, there is the age-old complaint by customers that adding drives is not as simple as picking up the commodity devices. Compellent, nor any other large manufacturer, supports the customer going out and buying an off-the-shelf seagate drive to pop in the unit. The variables are many and the risks are too high for data corruption.

However, I do think the vendors should cut down on the exorbitant rates they charge for add-on hardware if they truly want to market “future proof” value.

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This is the fourth of eight in a series titled 8 Must Haves for the IT Director

Number 4 – Automated Tiered Storage

Dynamically Classify and Migrate Data

To continue containing costs throughout the lifecycle of enterprise data, Dell Compellent leverages an
innovative data movement engine that integrates intelligent tiering with advanced virtualization.
Traditionally, information lifecycle management has been a tedious and manual process with no end.
Data is continually classified and reclassified based on its “importance” to the organization, an
approach rife with political implications.

Politics aside, manually moving data between high-performance drives and more cost-effective,
capacity-oriented drives is complicated and time consuming. Add-on migration engines can help, but
increase overall software costs and waste valuable staff time for systems integration. Either way, each
volume must be moved in its entirety, although some of that data is probably more frequently
accessed. That means administrators have to continuously fine-tune data placement over time. Still,
the alternative – retaining all enterprise data on high-performance drives – is not only costly in terms of
disk expenditures, but wastes energy and squanders limited data center space.

With Dell Compellent, since data is actively, intelligently managed at the block level, manually moving
data between tiers is a thing of the past. Using unique Automated Tiered Storage software, known as
Data Progression, Dell Compellent dynamically classifies and migrates data to the optimum tier based
on actual usage. The “importance” of data becomes a matter of fact according to actual usage, and
data placement organically remains in tune with changing business needs.

Data is written to high-performance Solid State (SDD) or Fibre Channel (FC) drives on Tier 1 storage.
Then, as the frequency of access declines, the less active blocks of data migrate to FC or SAS drives on Tier 2 storage. Over time, completely inactive data moves to high-capacity SAS or SATA drives on Tier 3 storage. To further free up high-performance drives for mission-critical applications, snapshots
automatically flow to cost-effective, energy-saving drives. Meanwhile, the most active data is
dynamically placed on the outer tracks of each drive for increased performance. Since most enterprise
data is inactive, on average organizations can reduce disk expenditures by as much as 80 percent with
Automated Tiered Storage.

Regardless of the current tier, with Dell Compellent storage, enterprise data always remains readily
available. Even once-inactive data is promoted to a higher tier if it becomes regularly accessed again.
Administrators simply customize the tiering algorithm according to specific organizational needs, or use
default settings established based on current industry best practices.

Next up in our 8 Must Have series is #5, Space Efficient Snapshots.

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You’re probably already familiar with Compellent’s modular architecture so I won’t bore you with pieces and parts of hardware. Suffice it to say you can build limitless Compellent configurations, but we’ve bundled a few basic ones here combining the SC040 controllers, disk enclosures and disk options. What’s key is the introduction of a super fast SAS back plane at the core of Storage Center 5.4.

Here’s The Storage Center 5.4 Highlights:

  • 6 Gb SAS drives provide twice the performance and use nearly half the power of 3 Gb SAS drives
  • 2.5″ SAS drives are two-thirds smaller than 3.5″ drives, resulting in a significant performance boost with a smaller footprint
  • 6 Gb SAS enclosures provide 24 bays to accommodate twice the number of spindles in the same amount of rackspace
  • Series 40 controller features more memory, six PCI-e slots and a battery-less cache, and provides 25% higher I/O performance
  • 10 Gb iSCSI and FCoE I/O cards and HBAs provide the latest industry-standard interconnect performance
  • Live Volume acts as a storage hypervisor, actively mapping one storage volume to two Dell Compellent arrays at the same time

I’d be curious to hear from Legacy customers that are running the new gear in parallel, or, if you’ve replaced older gear, how was the transition?

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