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.

Windows IT Pro Webinar - Should I defrag my SAN?

by Michael 4. May 2010 04:59

Later this month (Thursday, May 27, 2010 at 12:00pm Eastern / 9:00am Pacific), IT Analyst David Chernicoff and I will co-host a webinar covering the benefits and caveats of defragmenting SAN attached servers.

Here is the abstract: 

As storage technologies have become more advanced there is a tendency for storage administrators to believe that the hardware is handling all of their data maintenance needs, keeping their files optimized in the best possible way for top performance and availability. The reality is that hardware solutions alone aren't the most efficient way to keep your critical data stored in an optimal fashion. With this webinar we will give you the information you need to understand how your data is actually being handled and what you can do to improve the performance and optimization of your Windows Server storage.

You can register here: 

We also have two webinars planned for June on the topic of virtualization. One jointly with Redmond Mag, and the other with Microsoft. I'll post registration links on this blog when they are available. Lastly, we'll have a reprise of the SSD webinar we did with Microsoft sometime in July - this time we'll host and Microsoft will be our guest.


SAN | SSD, Solid State, Flash | virtualization

SAN defrag

by Michael 13. August 2009 03:01

Storage Area Networks (SANs) are becoming increasingly more common. A few years ago "SAN" was an acronym that rarely made it out of the lexicon of IT Storage Admins at 1000s+ employee multinationals. In more recent years the SAN IHV/ISVs have greatly simplified and reduced the installation, maintenance, technical effort, and acquisition costs. It's increasingly more common to see SANs in medium sized businesses. Many SAN providers have even offered targeted "mid-range" solutions often for those mid-sized organizations. EMC is one such vendor that targets just such a solution with their Clariion product line.

Microsoft has also been at the forefront of advancements in data storage centralization. Technologies like Storport (introduced in Windows Server 2003), iSCSI software initiator, multipath I/O storage stack, and more.

A great deal of innovative software from Microsoft and SAN vendors make the whole system work.

An important point to be aware of is where in the whole computer system, the SAN "plugs" in. A SAN is, in essence, a replacement for a single disk. In the Windows I/O storage stack a SAN solution replaces the disk driver (disk.sys), with its own drivers. Eventually data must reside on a physical storage device of some kind, so any request to read or write data will have to go through this disk driver, or SAN replacement thereof. However, before the I/O request gets to this lower level it goes through a local disk file system. When talking about Windows in a SAN, that local disk file system is pretty much always going to be NTFS. Fragmentation as Windows sees it and cares (same for Diskeeper), is at NTFS. So, if files are fragmented as NTFS sees it, the local disk file system has to send a great deal more I/O traffic into the SAN, causing the SAN to do more work that it should.

We have a very thorough white paper that covers defragmenting SAN. It also includes Best Practices for Diskeeper. Check it out here.

Even SAN vendors recommend defragmenting Windows. EMC includes a paragraph about the need for their Clariion family of products in a white paper here. In it (pg. 5) it says:

“File system fragmentation over time is almost inevitable. Performing defragmentation regularly keeps performance optimal. There are a number of host-based utilities that can perform defragmentation in place to accomplish this… (SnapView™, SAN Copy™ and LUN Migration will not defragment file systems)…” ... “Perform regular defragmentation of the file system to ensure optimal performance.”

The interesting part is they also note the SAN file system solutions they offer are NOT designed to handle NTFS fragmentation, and that they recommend to defragment that "local disk" file system. When we here at Diskeeper talk about the need to defrag SAN attached systems, were talking about doing what we always have done - defragging NTFS in Windows (from Windows). That is an important point as SANs also use a file system to organize data. Diskeeper, nor Windows defrag addresses this. "If" defrag of some kind is needed in this SAN file system it is handled by the SAN vendor - you can check with their support staff on that subject. Defragmenting NTFS and defrag of SAN file systems are two completely different subjects and should not be confused.

Even more reading:

Ziff Davis Enterprise (from the same parent company of eWeek) just released a paper on defragmenting SANs, including benefits and covering some considerations as well. You can read that here.

In summary, even with the tremendous amount of technology that has gone into SANs over the past decade, defragmenting SANs is still just as vital as defragmenting DAS (direct attached storage).

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