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Green Data Center Storage Part II

Sustained CostEffectiveness in Transitioning Times

Bruce Naegel John Colgrove

W. David Schwaderer

September 24, 2007

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Storage Network Security Executive Summary This is the second part of a threepart paper on Data Center Power and cooling. It discusses data and disk types and how to match data and disks effectively within information life cycles. In addition, it examines data growth problems and how they directly impact data center power and cooling considerations. The paper concludes with a discussion of tiered storage and how Symantec’s Veritas Storage Foundation Dynamic Storage Tiering can significantly reduce power and cooling requirements.



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Table of Contents

Executive Summary ........................................................................................................3 Table of Contents ............................................................................................................5 Different kinds of Data....................................................................................................7 Combining Data with Disk Types....................................................................................8 Disk Drive Growth........................................................................................................12 Data Growth Tyranny....................................................................................................12 MAID System Overview ...............................................................................................13 Three Tier Savings Potential..........................................................................................13 Aggressive Dynamic Storage Tiering (DST)..................................................................15 Part II Conclusion .........................................................................................................16 Appendix B – RAID Overview......................................................................................17 Appendix C – CC Storage Analysis Tool.......................................................................19



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Different kinds of Data As indicated in Part I, IT organizations support their enterprises according to pre determined SLAs. Some SLA terms require extremely fast access to selected data while allowing slower access for other data. Other SLAs might specify required data retention periods before the data can be discarded. Yet other SLA might specify different access speeds depending on time periods such as highspeed access during quarterend and year end reporting and slower access during other periods.

We now define transaction data as data that currently experiences high read, write, and update activity and therefore requires high performance storage. Nontransaction data is other data that does not currently experience such high activity and can reside on lower performance storage.

We have mentioned that Appendix B shows how different forms of RAID provide different performance levels. As it turns out, there are multiple types of hard disks that can also help meet the varying objectives that SLAs dictate. 1

Two generally recognized groups are:

High performance disks – These expensive disks provide lowlatency (fast) responses to read/write requests and high, sustained transfer rates (throughput). In every possible manner, this type of disk is highly optimized for high performance and well suited to store transaction data data involved in high transaction rate applications.

Typically, high performance disks have relatively modest capacities – 36.8 or 73.4 GBytes at the time of this writing. This modest capacity helps accelerate performance in several ways.

Internally, the storage platters can be very small, allowing them to spin faster and generate less air friction heat. The smaller disks naturally decrease the distance the readwrite arm moves to perform operations. In addition, the faster rotation rate and faster electronics increases the media transfer rate, which increases the throughput.

Finally, smaller capacities and higher sustained transfers allow applications to read all data on a disk in a relatively short time, say, less than 20 minutes. This is important in backup operations and RAID data recovery rebuild operations.

But, high performance disks require relatively substantial power for their modest storage capacities. And this substantial power generates substantial heat. High performance disks are therefore both expensive to buy and expensive to operate.

1 While the IT industry attempts to place any disk into one of two groups, the large population of available models provides a continuum of performance and capacity tradeoffs.



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The only visible relief in this situation is an eventual migration to 2.5” high performance disks which can use as much as 40 percent less power.

High capacity disks These relatively inexpensive disks are highly optimized to provide substantially more (e.g.10X) storage capacity than high performance disks while consuming lower total power. Their storage platters are bigger and spin slower, thereby reducing air friction heat and helping keep them from tearing themselves apart.

Consequently, high capacity disks have higher access latency and slower sustained transfer times. But, because they require substantially less power, their consumed Watts per GByte ratio is much more favorable than high performance disks achieve though they can rarely meet the performance level high performance disks exhibit.

Historically, the IT industry has regarded high capacity disks as being less reliable than high performance disks enterprises often use. Interestingly enough, a recent Carnegie Mellon University’s Computer Science Department report titled Disk failures in the real world: What does an MTTF of 1,000,000 hours mean to you? suggests that high capacity disks have reliability comparable to high performance disks, much to the surprise of the IT industry. The report indicates that they detected “little difference in replacement rates between SCSI, Fibre Channel and SATA drives, potentially an indication that diskindependent factors, such as operating conditions, affect replacement rates more than component specific factors."

Combining Data with Disk Types We have seen that different enterprise data has different application response and protection requirements, dictated by associated SLAs. Moreover, different disk types have different performance and capacity requirements. Finally, different RAID variants provide different performance and protection levels.

Transaction data is well suited to RAID 0+1 protection using performanceoriented drives, requiring an additional 100 percent more disk capacity.

Nontransaction data is well suited to RAID 5 or RAID 6 protection using capacityoriented drives. RAID 5 (4+1) systems require an additional 25 percent more disk capacity and RAID 6 (4+2) systems require an additional 50 percent more disk capacity

While it can prove tempting to place transaction data on capacityoriented drives, it is important to know that the drives may not physically allow applications to meet the application SLAs. This is a careerlimiting train to miss.



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Figure 2 illustrates the concept.

Figure 2 – Matching Data Types with Appropriate Drives to meet SLAs

In examining Figure 2, there are two storage tiers resulting from various SLA requirements. The upper tier is called Tier 1 and the lower tier is called Tier 2.

Note that this is a rather simplistic rendering because there are a variety of disk drive models with different performance and capacity tradeoffs as well as several RAID variants that can collectively combine to provide a continuum of different application performance levels.

RAID 0+1 Mirrored Transaction

Data

RAID 5 (4+1) NonTransaction

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Performance Drives

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In addition, Figure 2 also fails to depict the snapshot and backup information automated processes create for disaster and error recovery. Figure 3 therefore depicts a closer look at Tier 1, representing backup and snapshot data as shaded figures.

Figure 3 – Mirrored Tier 1 data from Figure 2 with recovery snapshots and backup copies unnecessarily consuming Tier 1 capacity.

Now, the best snapshot and backup information an enterprise can have is snapshot and backup information that is never used because potential failures never occurred. Therefore, recovery data can often reside in Tier 2 where it is available with reasonable access speed and more economically stored.

However, the reality is that such snapshot and backup information often resides in the same tier where the original information resides, unnecessarily consuming copious high performance storage capacity while simultaneously consuming increasingly expensive electric power. Both resources are usually in short supply, becoming scarcer and more expensive every day.

The solution is to migrate as much data as possible as soon as possible from the top tier to the lower tier. This is easily accomplished by using Symantec’s Storage Foundation Dynamic Storage Tiering (DST) feature, Veritas Volume Manager (VxVM), and CC Storage products. These products interoperate with many leading storage subsystem offerings from different vendors that provide Tier 1 and Tier 2 data storage support.

Dynamic Storage Tiering provides continuous migration support for file system data (not data contained within database structures) using automated methods that respond to changing conditions. Conversely, Veritas Volume Manager and CC Storage provide scheduled data migration services for both file system data and data contained within database structures. Collectively, these offerings provide effective enterprise data migration capability backandforth between tiers.



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Symantec also has other products (e.g. CC Storage and Storage Foundations Volume Manager) that can identify storage migration candidates as well as tools to help migrate the data. These will be described in more detail in an update to this white paper.

Too Many Data Copies

Enterprises usually retain too many data copies. Mirroring may protect mission critical application data which is also probably protected by another replica in a disaster recovery (DR) datacenter. The DR replica is likely also mirrored, making four total copies at this point.

Next, enterprises often have a surprising number and variety of snapshots as well as other data copies. Some copies:

• enable accelerated backup and recovery • are available for data mining or endofperiod processing • enable data transformations to move data between applications • exist as safety precautions before various administrative operations • are available for testing and development

Often snapshot operations create the copies, leaving them in the same high performance disk array as the original data. Often they are also mirrored or otherwise protected at the same RAID level as the production data because it is operationally easier to configure snapshot storage the same way as the production storage.

In typical customer environments Symantec often sees from 10 to 30 copies of each production data byte. Many of these copies are no longer needed or are misplaced and the enterprise does not even know they still exist. Clearly, reducing the number of data copies reduces storage capacity requirements and storage power consumption. Once reduced, Symantec’s Veritas Volume Manager (VxVM) can move snapshots and other copies from Tier 1 performance arrays to Tier 2 capacityoriented arrays.

Pareto’s Law Since data accesses often follow Pareto’s Law – 80% of data accesses involve only 20% of the data – aggressively migrating effectivelydormant application and application recovery data from Tier 1 to Tier 2 usually meets application performance SLAs while liberating substantial Tier 1 capacity – sometimes as much as 80%. The trick is to know what data to migrate and when. This is possible by using Symantec analysis tools such as CC Storage. CC Storage enables Symantec customers to identify storage for migration, saving them both capital costs and power after the migration.



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As indicated earlier, through purposebuilt construction, the lower Tier 2 usually cannot exhibit the highspeed application performance that the upper tier exhibits. So, migrating data from Tier 1 to Tier 2 must proceed judiciously to ensure continuous SLA fulfillment.

In this respect, migration can therefore seem like performing inflight airplane engine maintenance. Symantec has therefore developed a firstapproximation tool that measures file accesses to help identify what data should migrate. Appendix C briefly discusses this tool which is available on the Symantec Technical Network (STN).

If desired, released storage capacity can be removed to save data center electricity and space. Alternately, consolidated and unused Tier 1 storage can be powered off and left in place, thereby saving as much as 80% of Tier 1’s relatively high electrical requirements. Leaving the unused storage in place when possible provides future and emergency Tier1 storage expansion while deferring capital outlays.

Disk Drive Growth

While disk storage capacity naturally increases with each areal density (bit density) increase, data is growing far faster and will be for the foreseeable future. Hence, the total number of disk drives an enterprise needs necessarily grows commensurately simply from storage capacity requirements.

However, performanceoriented disks are not increasing their I/O Operations/second (IOPs) nearly as fast as disk capacity increases. Consequently, this further increases the required number of disks many applications have increasing IOP requirements in addition to increasing storage needs. Since the number of disk drives and array subsystem DRAM cache amounts primarily determine storage power consumption, the power consumption situation will likely become worse. Here, it is important to note that most Tier 1 arrays presently use 36 GByte or 73 GByte disk drives because of stringent I/O Operations/second (IOPs)SLA performance requirements. Though new performanceoriented Tier 1 arrays may arrive with 146 GByte drives, many data centers also likely have existing legacy arrays in service that use 36 GByte drives or, perhaps, even 18 GByte drives.

From a power and cooling perspective, it may appear tempting to replace, say, eight older arrays that use 18 GByte drives, with one new array that uses 146 GByte drives and has the equivalent storage capacity with 1/8th the drives. However, 18 GByte drive IOPs performance nearly equals 146 GByte drive IOPs performance. So the IOPs performance loss would likely be too great with such a new, single array. Finally, other considerations such as the actual environmental impact of building new equipment to replace working, lessefficient equipment further exacerbate migration challenges.

Data Growth Tyranny



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Because of continuing data growth, any existing data storage subsystem will eventually exceed available capacity unless more capacity becomes available. However, the data center may eventually not have enough space or electric power to support expanded storage capacity. This is the point where enterprises begin to consider building a new data center that can easily cost tens or hundreds of millions of dollars over time.

Clearly what is required is a different level of thinking than the incremental one used to arrive at this situation. That solution involves expanding Tier 2 capacity with extremely high capacity disks. But that consumes increasing space and power because data is growing faster than disk capacity is.

Moreover, unlike Tier 1 storage, traditional Tier 2 storage has no place to migrate data to that would free Tier 2 storage capacity and allow enterprises to remove or power off storage devices. An alternative solution augments traditional Tier 2 storage capacity with a storage resource that is optimized to provide high capacity storage capacity while simultaneously consuming minimal electrical power. That approach is available in the form of Copan Systems’Massive Array of Inactive Disks (MAID) technology.

MAID System Overview The Storage Networking Industry Association (SNIA) defines a MAID system as:

A storage system comprising an array of disk drives that are powered down individually or in groups when not required.

Copan’s MAID system also provides massive storage capacity in minimal space by housing disks in a three dimensional array versus a two dimensional array found in many storage systems. Like all MAID systems, Copan’s massive storage system consumes a small fraction of the electric power that equivalent capacity, traditional Tier 2 storage systems require.

Three Tier Savings Potential In effect, MAID systems provide a third data storage tier to migrate data to from the second tier in traditional twotiered systems. Data residing on a MAID system is not archived in the traditional sense because it is readily accessible to applications as though it was on a Tier 2 high capacity data storage subsystem.

The difference is that MAID storage subsystems electrically poweroff idle disks and powers them back on when an application needs access to the dormant data. This approach is similar to sensors that turn room lighting on and off depending on whether anyone is in the room. There is a slight initial access delay, usually less than 30 seconds, before the data is available. Thereafter, applications usually enjoy standard Tier 2 access performance.

Because of this slight delay, the type of data that a MAID system best stores is data that must be readily available, albeit with a longer access latency, but is not likely to



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experience high access rates. The storage industry refers to online data with such negligible access activity as persistent data.



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Aggressive Dynamic Storage Tiering (DST) With a MAID Tier 3 data storage system and aggressive migration to lower tiers using Veritas Storage Foundation’s Dynamic Storage Tiering (DST) feature, it is possible to significantly reduce the amount of data stored in traditional Tier 1 and Tier 2 configurations.

Within many enterprises today, Tier 1 might have 20% of the total data and Tier 2 might have 80%. Through aggressive DST, this can become, say, 5% in Tier 1 and 95% in Tier 2. By introducing MAID storage as third tier and applying aggressive DST to Tier 2, this may result in 5% at Tier 1, 20% in Tier 2, and 75% in Tier 3 and substantially reduced electrical power requirements.

While Tier 2 may use the same capacity drives as Tier 3 MAID system, therefore exhibiting a similar storage density (i.e. space efficiency expressed as GBytes per data center square foot) as Tier 3, Tier 3 substantially reduces the electrical power traditional Tier 2 requires because it stores infrequently accessed data on disks that are usually powered off.

Powerwise, Tier 3 would therefore be more economical than Tier 2 storage because it requires significantly fewer watts per GByte. Note that it is also possible for Tier 3 storage to reside in a different data center, thereby further reducing space and electrical requirements in crowded or underpowered primary data center facilities. Finally, it is important to approximate the potential power savings between tiers. Since power is proportional to the number of disk drives, their characteristics (IOPS and capacity), and individual power consumption, Tier 2 is often 8 times more efficient (6x space per drive times 30% power difference plus a little cache). Similarly, Tier 3 is often 6 times as efficient as Tier 2 – it uses same disks but powers most disks off most of the time).

Therefore, it seems reasonable that combining this tier efficiency difference and improving utilization likely saves more than half the power used for storage in almost any environment.



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Part II Conclusion Controlling data center power and cooling requirements for storage subsystems requires an in depth understanding of an enterprise’s information life cycle. Once obtained, enterprises can match data types correctly to disk types and develop data tiering policies that achieve goals within SLA objectives.

The next and final part of this series discusses server energy savings and how to begin migrating to Green Data Center Storage and translates energy savings into operational savings.



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Appendix B – RAID Overview There are many forms and variants of RAID. Here are some of them:

While providing no protection against disk failure, RAID 0 spreads data uniformly across a number of disks. This is useful when many users need simultaneous access to a data such as a shared database. Here, spreading the data out across many disks allows multiple overlapped concurrent accesses though the probability of data loss increases with each additional disk used.

RAID 1 stores data in the necessary disk space and simultaneously makes one or more copies of the data on other disks. So, the multiple copies occupy much more disk capacity as the actually data values require. Clearly, there is a difference between the total amount of data an enterprise has and how much disk space the data requires.

RAID 0+1 combines RAID 0 and RAID 1. A data set resides on multiple disks and a second, independent set of disks contains mirror copies of the data. The mirroring provides protection against the loss of disks, and using twice as many disks allow twice as many concurrent accesses, greatly accelerating performance.

RAID 5 similarly spreads data across a number of disks, say four, and then uses the data to create a checksum value that can reconstruct lost data if one of the four disks fails. The storage subsystem can store the value on a fifth disk drive but usually uses the five drives together, spreading the data and checksum information across the set of disks.

Like RAID 5, RAID 6 spreads data across a number of disks, say four, and then uses the data to create two or more checksum values that can reconstruct lost data if more than one the four data disks fails. The storage subsystem can store the value on a fifth and sixth disk drive but usually uses the drives together, spreading the data and checksum information across the set of disks.

Clearly, there is a difference between the total amount of data an enterprise has and how much disk space the data requires.

Calculating various RAID Capacity Factors

The formula to compute a RAID set capacity factor is:

(Total Drives in the RAID set) / # of Data Drives



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RAID 1: RAID 1 replicates data. A 2way mirror has 2X the total number of drives as compared to data drives. A 3way mirror has 3X the number of drives. These yield 2X and 3X capacity factors respectively. This scheme also applies to RAID 0+1 or 1+0 that combines striping and mirroring.

RAID 5: RAID 5 is usually a number of data drives plus one additional parity drive that completes the RAID set. A RAID set with 5 data drives and one parity drive has 6 drives total and 5 data drives worth of capacity

RAID 6: RAID 6 has 2 parity drives per RAID set. So a RAID set with 5 data drives would have 7 total drives / 5 data drives or a RAID capacity factor of 7/5.

I/O Performance Measurements:

Many factors affect I/O performance. Two primary factors are the total number of disk drives and individual disk drive performance. A future revision of this white paper will address this topic in more detail.



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Appendix C – CC Storage Analysis Tool

CC Storage is a Storage Area Network (SAN) hardware management and monitoring application that discovers SAN resources switches, Host Bus Adapters (HBAs), disk arrays, host servers, and applications.

CC Storage also has the ability to monitor file system activity and determine which files are active and inactive, hence eligible for archiving or migration to more energy efficient storage devices (Figures C1 through C4). In addition to understanding where the inactive files are, CC Storage can also help to reconfigure the SAN and help move the data to more appropriate storage. Data administrators can identify inactive data on Tier 1 storage and help to migrate it to the Tier 2 storage using SAN reconfiguration by:

Opening a connection between the source and the destination Copying the data to Tier 2 Closing the connection.

Thus, CC Storage is a powerful primary storage subsystem management tool that enable enterprises to reduce power and cooling costs significantly through increased storage utilization.



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Figure C1 – CC Storage File System Analysis Screen Shot

Figure C2 – CC Storage File Aging Summary Report



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Figure C3 – CC Storage File Types Usage Summary Report

Figure C4 CC Storage File Tpes Aging Summary – By File Types Modified Report



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About Symantec Technology Network (STN)

Symantec Technology Network (STN) is Symantec Corporation’s technical information generation and dissemination organization. It distributes a free monthly technical newsletter that discusses timely technology events to 120,000 email subscribers across the globe. STN also publishes technical data storage and security articles each month for large enterprise and Small and Medium Business (SMB) readers, as well as hosts a variety of blogs and product discussion forums discussing Symantec product tips and insights. To subscribe to STN’s Technical Newsletter and review other STN materials, please visit STN at:

http://www.symantec.com/enterprise/stn/index.jsp

About the Authors

Bruce Naegel

Bruce Naegel is a Senior Product Manager in Symantec’s Data Center Management Group. He has been in various positions in Storage Product Management for over 20 years, spanning companies from 10 employees to 100,000. During that tenure, he participated in a number of award winning product releases. He has authored a number of published articles, delivered numerous mass storage presentations and been active in various Mass Storage Software standards bodies. He also has an active interest in kaleidoscopic photography.

John Colgrove

John Colgrove is a Symantec Fellow and Vice President.

W. David Schwaderer

W. David Schwaderer is the Symantec Technology Network (STN) EditorInChief.

He has authored six commercial software programs and ten technical books including Data Lifecycles—Managing Data for Strategic Advantage published by John Wiley & Sons Ltd. His soontobepublished eleventh book is titled Innovation Survival— Concept, Courage and Change. He is also working on a twelfth book titled Data Center of the Future that examines the tectonic forces reshaping today’s enterprise data centers.

David has a Masters Degree in Applied Mathematics from the California Institute of Technology and an MBA from the University of Southern California. He lectures at Stanford on the subject of innovation.

http://www.symantec.com/enterprise/stn/index.jsp



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