Condusiv Technologies Blog

Condusiv Technologies Blog

Blogging @Condusiv

The Condusiv blog shares insight into the issues surrounding system and application performance—and how I/O optimization software is breaking new ground in solving those issues.

3 Min Video on SAN Misconceptions Regarding Fragmentation

by Brian Morin 23. June 2015 08:56

In just 3 minutes, George Crump, Sr Analyst at Storage Switzerland, explains the real problem around fragmentation and SAN storage, debunks misconceptions, and describes what organizations are doing about it. It should be noted, that even though he is speaking about the Windows OS on physical servers, the problem is the same for virtual servers connected to SAN storage. Watch ->

In conversations we have with SAN storage administrators and even storage vendors, it usually takes some time for someone to realize that performance-robbing Windows fragmentation does occur, but the problem is not what you think. It has nothing to do with the physical layer under SAN management or latency from physical disk head movement. 

When people think of fragmentation, they typically think in the context of physical blocks on a mechanical disk. However, in a SAN environment, the Windows OS is abstracted from the physical layer. The Windows OS manages the logical disk software layer and the SAN manages how the data is physically written to disk or solid-state.

What this means is that the SAN device has no control or influence on how data is written to the logical disk. In the video, George Crump describes how fragmentation is inherent to the fabric of Windows and what actually happens when a file is written to the logical disk in a fragmented manner – I/Os become fractured and it takes more I/O than necessary to process any given file. As a result, SAN systems are overloaded with a small, fractured, random I/O, which dampens overall performance. The I/O overhead from a fragmented logical disk impacts SAN storage populated with flash equally as much as a system populated with disk.

The video doesn’t have time to go into why this actually happens, so here is a brief explanation: 

Since the Windows OS takes a one-size-fits-all approach to all environments, the OS is not aware of file sizes. What that means is the OS does not look for the proper size allocation within the logical disk when writing or extending a file. It simply looks for the next available allocation. If the available address is not large enough, the OS splits the file and looks for the next available address, fills, and splits again until the whole file is written. The resulting problem in a SAN environment with flash or disk is that a dedicated I/O operation is required to process every piece of the file. In George’s example, it could take 25 I/O operations to process a file that could have otherwise been processed with a single I/O. We see customer examples of severe fragmentation where a single file has been fractured into thousands of pieces at the logical layer. It’s akin to pouring molasses on a SAN system.

Since a defragmentation process only deals with the problem after-the-fact and is not an option on a modern, production SAN without taking it offline, Condusiv developed its patented IntelliWrite® technology within both Diskeeper® and V-locity® that prevents I/Os from fracturing in the first place. IntelliWrite provides intelligence to the Windows OS to help it find the proper size allocation within the logical disk instead of the next available allocation. This enables files to be written (and read) in a more contiguous and sequential manner, so only minimum I/O is required of any workload from server to storage. This increases throughput on existing systems so organizations can get peak performance from the SSDs or mechanical disks they already have, and avoid overspending on expensive hardware to combat performance problems that can be so easily solved.

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NEW V-locity 4 VM Accelerator Improves VM Performance by up to 50%

by Jeff Medina 10. December 2012 10:00

Today we are very excited to announce the release of V-locity 4 VM Accelerator. With this latest release, V-locity increases VM and application performance by up to 50% and does so without any additional storage hardware.

Let’s face it - in today’s world of virtual environments, we generate a tremendous amount of data and it’s only the beginning. In fact, findings included in a recent study by IDC titled “Extracting Value from Chaos” predict that in the next ten years we will create 50 times more information and 75 times more files.

The impact of this data explosion on server virtualization can often lead to I/O bottlenecks. This is because a physical server running multiple virtual machines (VMs) must often carry out far more I/O operations than one server running a single workload, and typical virtualization environments emulate I/O devices that run less efficiently than native I/O devices.

In essence, virtualization acts like a funnel, combining and mixing many disparate I/O streams, sending out to the disk what becomes a very random I/O pattern. To make matters worse, the more VMs are added, the more the issue is compounded as more I/O is "randomized." All of this has a very negative affect on storage performance, and renders time-honored techniques such as read-ahead buffers and caching algorithms far less effective than in conventional physical environments.

Storage I/O is the most critical issue in a virtualized environment, and can cause organizations to spend a great deal on storage, purchasing more and more disk spindles, but often using only a fraction of their capacity because of performance issues. The outcome is that, due to issues relating to performance bottlenecks in the storage infrastructure, some applications are deemed unable to be virtualized; however, a properly tuned storage environment might have accommodated those applications. So what’s the alternative? The answer is V-locity 4 VM Accelerator. 

V-locity 4 VM Accelerator provides:

  • Increased application performance up to 50%
  • Up to 50% faster access to frequently accessed files
  • Faster I/O performance without the cost of additional storage hardware
  • Increased VM density per physical server up to 50%
  • Extended hardware lifespan by eliminating unnecessary I/Os
  • Automatic and real-time operation for true “Set It and Forget It®” management 

What makes V-locity 4 so effective is its powerful toolkit of proactive technologies, including IntelliWrite,® V-Aware,® CogniSAN,® InvisiTasking® and the new IntelliMemory® RAM caching technology.

New! IntelliMemory™ Caching Technology
IntelliMemory intelligent caching technology boosts active data, improving I/O response time up to 50% or more while also eliminating unnecessary I/O operations from getting into the network or storage.

Improved! IntelliWrite® Technology
IntelliWrite automatically prevents the operating system from breaking files into pieces and writing those pieces in a performance penalized manner. This proactive approach improves performance up to 50% or more while preventing any negative impact to snapshots replication, data deduplication or thin provisioning growth. As this proactive approach happens at the server level, the network and shared storage simply has less I/O operations to transfer and process.

New! Performance Benefit Analyzer
The Performance Benefits Analyzer helps document the performance benefits of V-locity. The benefit analyzer looks at your current system performance, then compares these results to those after using V-locity to provide a detailed report showing specific improvements and benefits to your system.

V-Aware® Technology
V-Aware detects external resource usage from other virtual machines on the virtual platform and eliminates resource contention that might slow performance.

CogniSAN® Technology
CogniSAN detects external resource usage within a shared storage system, such as a SAN, and allows for transparent optimization by not competing for resources utilized by other VMs over the same storage infrastructure. And it does this without intruding in any way into SAN-layer operations.

InvisiTasking® Technology
InvisiTaksing allows all the V-locity 4 "background" operations within the VM to run with zero resource impact on current production.

Set It and Forget It®
Automatic and real-time operation.

For more details and a FREE trial, visit or call a sales representative at 1-800-829-6468.

Best Practices for Storage Area Network (SAN) Defragmentation

by Michael 29. March 2011 02:30


As high performing storage solutions based on block protocols (e.g. iSCSI, FC), SANs excel at optimizing block access. SANs work at a storage layer underneath the operating systems file system; usually NTFS when discussing Microsoft Windows®. That dictates that a SAN is unaware of “file” fragmentation and unable to solve this issue.

Fig 1.0: Diagram of Disk I/O as it travels from Operating System to SAN LUN.

With file fragmentation causing the host operating system to generate additional unnecessary disk I/Os (more overhead on CPU and RAM) performance suffers. In most cases the randomness of I/O requests, due to fragmentation and concurrent data requests, the blocks that make up the file will be physically scattered in uneven stripes across a SAN LUN/aggregate. This causes even greater degradation in performance.

Fig 1.1: Sample Windows Performance Monitor Report from fragmented SAN-attached NTFS volume.

Fortunately there are simple solutions to NTFS file system fragmentation; fragmentation prevention and defragmentation. Both approaches solve file fragmentation at the source, the local disk file system.

IntelliWrite® “The only way to prevent fragmentation before it happens™”

IntelliWrite is an advanced file system driver that leverages and improves upon modern Windows’ file system “Best Fit” file write design in order to write a file in a non-fragmented state on the initial write. Intelligently writing contiguous files to the disk provides four principal benefits above and beyond defragmentation, including:

  • Prevents most fragmentation before it happens
  • Better file write performance
  • An energy friendly approach to improving performance, as defragmentation is not required for files handled by IntelliWrite
  • 100% compatibility with copy-on-write technologies used in advanced storage management solutions (e.g. snapshots)

While eliminating fragmentation improves performance. it is important to properly configure and account for advanced SAN features.

With the increasing popularity of SANs, we've included instructions in the Diskeeper installation to ensure users properly configure Diskeeper:

We suggest reading this full document before executing any of the recommended configurations. These instructions apply to V-locity (used on VMs as well).

Best Practices:


Implementing Diskeeper on a SAN is simple and straightforward. There are two principal concepts to ensuring proper configuration and optimal results:

  • Ensure IntelliWrite is enabled for all volumes.
  • Find a time to schedule Automatic Defragmentation (more details below)

If you are implementing any of the following SAN based technologies such as Thin Provisioning, Replication, Snapshots, Continuous Data Protection (CDP) or Deduplication, it is recommended to follow these guidelines.

Defragmentation can cause unwanted side effects when any of the above referenced technologies are employed. These side effects include:

With SAN replication:
Likelihood of additional data replication traffic.

With Snapshots/CDP:
Likelihood of additional storage requirements for data that defragmented/moved and snapshot-related performance lag.

With Thin Provisioning:
Likelihood of additional storage requirements for data that defragmented/moved.

With Deduplication:
Potential for additional deduplication overhead. Also note that deduplication can be used to remove duplicate blocks incorrectly allocated due to defragmentation. This process can therefore be used to reclaim over-provisioned space.

This is why it is important to enable the fragmentation prevention (IntelliWrite) and change the Automatic Defragmentation to occur during non-production periods to address the pre-existing fragmentation:

During Installation, disable Automatic Defragmentation;

Uncheck the “Enable Automatic Defragmentation” option during installation.

Upon installation ensure IntelliWrite is enabled on all volumes (default). IntelliWrite was specifically designed to be 100% compatible with all advanced SAN features, and should be enabled on all SAN LUNs. IntelliWrite configuration is enabled or disabled per volume, and can be used in conjunction with Automatic Defragmentation, or exclusively.

To ensure IntelliWrite is enabled, right click a volume(s) and select the feature.

Then confirm “Prevent Fragmentation on this volume” is selected, and click “OK” to complete.

Once installed, enable Automatic Defragmentation for any volumes that are not mapped to a SAN LUN. This may include the System Partition (e.g. C:\).

To enable Automatic Defragmentation, right click a volume(s) and select the feature.

Then check “Enable Automatic Defragmentation on the selected volumes” and click “OK” to complete.

If you are not using any advanced SAN features, it is recommended to enable Automatic Defragmentation for all days/times. However, note that pre-existing fragmentation will require significant effort from Diskeeper to clean up. This effort will generate disk I/O activity within the SAN.

Therefore, if existing fragmentation is significant, initially schedule Diskeeper to run during off-peak hours. As Diskeeper has robust scheduling capability, this is easily configured.

To enable Automatic Defragmentation during non-production periods, right click a volume(s) and select the feature.

Then check “Enable Automatic Defragmentation on the selected volumes”. Diskeeper is then scheduled by using your mouse to highlight over the 30 minute blocks in the interactive weekly calendar.

The above example disables defragmentation Monday through Friday. It also disables defragmentation Saturdays and Sundays except between 7pm until 3:30am the following morning. This would afford 17 hours of defragmentation availability per week. Immediately following these scheduled defragmentation periods is when SAN maintenance for advanced features should be addressed (e.g. thin reclamation, deduplication).

Should accommodating SAN maintenance be difficult (e.g. limited maintenance windows)using a weekly optimization process, very granular scheduling is also available with Diskeeper. Note, maintenance windows are not required in order to implement and benefit from IntelliWrite.

To schedule for specific non-reoccurring dates and times in the future, select the “Turn Automatic Defragmentation on or off based on specific dates” option. Click any multitude of dates and times using Shift-Select or Ctrl-Select. Once done, click OK to complete.

If you are implementing the above mentioned advanced technologies and your SAN provides hot block optimization / data tiering, it is also recommended to disable I-FAAST® (Intelligent File Access Acceleration Sequencing technology). I-FAAST sequences hot “files” (not blocks) in a Windows volume, after determining hardware performance characteristics. The sequencing process creates additional movement of data for those advanced SAN features, and is therefore generally recommended to disable when similar SAN solutions are in place.

To disable I-FAAST, right click a volume(s) and select the feature.

Note, I-FAAST requires Automatic Defragmentation be enabled. Also note that I-FAAST is disabled by default in Diskeeper 2011 in certain cases. Also note that I-FAAST generates additional disk I/Os and will therefore cause an increase in the aforementioned Automatic Defragmentation side effects.

Once pre-existing fragmentation has been removed, increase the periods in which Diskeeper actively optimizes the Windows file systems. With real-time defragmentation and InvisiTasking® technology, Diskeeper immediately cleans up fragmentation (that is not prevented by IntelliWrite). This minimal ongoing optimization generates only invisible, negligible I/O activity.

New features in Diskeeper 2011 to improve SAN performance:

Diskeeper 2011 introduces SAN specific solutions. These default solutions automate many of the configurations required for SAN-attached servers.

Diskeeper 2011’s new Instant Defrag™ technology dramatically minimizes I/O activity, and exponentially speeds up defragmentation. The Instant Defrag engine is provided fragmentation information, in real-time, by the IntelliWrite file system filter driver (those fragments that it does not prevent). Without the traditional need to run a time and resource intensive whole-volume fragmentation analysis, Instant Defrag can address the recently fragmented files as they occur. This dynamic approach prevents a buildup of fragmentation, which could incur additional I/O overhead to solve at a later date/time.

Diskeeper 2011’s new Efficiency Mode (default) maximizes performance, while minimizing disk I/O activity. By focusing on efficiency and performance and not on presenting a “pretty disk” visual display, Diskeeper 2011 minimizes negative side effects (e.g. reduce snapshot storage requirements or thin LUN growth, etc..) while maximizing performance benefits. It is a SAN-optimized defrag mode and our recommended solution for SAN-attached Windows volumes.

By default, Efficiency Mode also disables proprietary file placement features such as I-FAAST.

Also, by default, Diskeeper 2010/2011 moves data to lower NTFS clusters, and hence generally “forward” on SAN LUNs.

Best Practices Summary:
  • Ensure IntelliWrite is enabled for all volumes.
  • Automatic Defragmentation should be enabled at all times for all direct attached storage volumes.
  • Use Efficiency Mode of Diskeeper 2011.
  • Schedule Automatic Defragmentation on SAN LUNs, based on use of advanced SAN features.
  • Run SAN processes such as space reclamation and/or deduplication on recently defragmented LUNs using advanced SAN features.

Want this in PDF form. Get it here: Best Practices for using Diskeeper on Storage Area Networks.pdf (3.00 mb)

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Defrag | Diskeeper | SAN

Do you need to defragment your SAN?

by Michael 11. January 2011 13:04

I recently came across an older article about defragmenting SANs (read it here). It includes interviews with analysts, SAN vendors (some pro-defrag, some against), and an employee from Diskeeper Corporation.

I was particulary impressed with the EMC'ers response:

"The SAN can't do anything about the fact that Windows sees the file in 30 bits," said Wambach. "That's really something that is happening outside of the storage realm."

He highlights the abstraction perfectly.  SAN vendors claim that a defragmenter cannot correct fragmentation due to the fact it is abstracted from the physical blocks. We absolutely agree with this statement. And for that same reason, SANs cannot fix fragmentation in the NTFS file system, which causes excess and unnecessary overhead on the OS.


Storage VMotion and GOS fragmentation

by Michael 3. December 2010 06:57

I had a test run here internally in order to make a point about what does, or more specifically "does not", happen when you VMotion/SVMotion a Windows Guest OS (GOS). We wanted to demonstrate that, while VMware is copying the VM to another host/storage, it does nothing about the internal fragmentation of files in Windows.

We felt this was a valuable demonstration as one of the old (1980s) ways to "fix" fragmentation was to copy off the files/backup, reformat the volume, and then copy back/restore. This offered a degree of success, but required taking the data offline in order to get rid of most of the fragmentation. On a side note, backing up/copying fragmented files takes a lot longer than it would on contiguous and ordered files.

Anyway, S/VMotion is such a cool feature because it works on live VMs. So, if the VMDK movement somehow did align/reorder files in Windows, it could be a great solution to Windows file system fragmentation! So here's how we tested...

1. Setup 2 ESX 4.1 Servers with iSCSI storage and vCenter with SVMotion capability.

2. Create a VM with Windows 7 in one of the ESX Server storage (Ex: Storage1) and a 20 GB Thin virtual disk.

3. Using an internal tool, create moderate fragmentation on the virtual disk (80k fragments, average fragments per file around 3.0, around 50% free space).

4. Install V-locity with all features (e.g. defrag, IntelliWrite, etc...) disabled. This is just so we can run a fragmentation analysis and save the reports.

5. Save the "Before SVMotion" analysis report, and then stop V-locity Windows Service (to make sure it is entirely inactive).

6. Using SVMotion move the live VM to the other ESX Server storage (Ex: Storage2).

7. Once the move is completed, restart the V-locity Windows Service and perform a post "After SVMotion" analysis.

8. Save this job report.

We saw what we expected, given VMotion leverages Changed Block Tracking (CBT) technology and is block, not file based. I attached the report, so you can see the side-by-side analysis data, files in Windows are not defragmented in an SVMotion. Now, that's not to say possible fragmentation of the VMDK files themsleves (on VMFS datastores) was not affected, but that's a topic for another post. 

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