First, let’s clarify just which products and capabilities Symantec is offering here:

• Veritas Storage Foundation version 5.0MP3 for Unix/Linux includes SmartMove and the Thin Reclamation API
• Veritas Storage Foundation for Windows 5.0 only includes SmartMove at this point, but it will be updated to include Thin Reclamation at some point in the coming year

Although there is no real information on Symantec’s web site about all this yet, Symantec’s director of Storage Management and High Availability, Sean Derrington, assures me that their software is available now. Although no compatible arrays are in end-user hands, 3PAR will update their T-Class firmware to support the API shortly, and HDS and HP are on the way as well.

Thin Aware Software

Next, contrary to what I inferred from the announcement, there is no native thin provisioning capability in the file system or volume manager. So the first item in my list is right out. However, the volume manager is now “thin aware”, which means that it will communicate up to the file system and down to the array to coordinate more effective use of space.

When the volume manager is used with Veritas File System (VxFS) on UNIX or NTFS on Windows Server 2003 or 2008, it will automatically keep track of deleted files and will pass this information down the stack to the array. This is a major piece of functionality to add, especially to NTFS, “hole punching” (like NetApp) to maximize thin provisioning.

The Storage Foundation tools have also been updated to properly report on thin provisioned volumes. For example, the following screenshot shows three disk devices where encl1 supports thin reclamation and encl0 does not.

# vxdisk list
DEVICE        TYPE   DISK          GROUP         STATUS
encl0_0       auto   encl0_0       mydg online   thin
encl1_0       auto   encl1_0       mydg online   thinrclm
encl1_1       auto   ecnl1_1       mydg online   thinrclm

Thin Reclamation API

The Veritas Thin Reclamation API allows the Storage Foundation volume manager and file systems to communicate with thin-capable arrays when data is deleted on thin-ified LUNs, maintaining their thin-ness as you go. When a file is deleted, the file system will communicate to the volume manager that that space is no longer needed. When the server administrator runs the “vxdisk reclaim” or “fsadm –R” commands, the volume manager will communicate this information to the array (using SCSI commands) that any vacated disk blocks can now be reclaimed. Symantec expects folks to set up a cron job to reclaim space, or perhaps just run it when they see the need.

This is brilliant stuff, and ought to make thin provisioning shine in terms of array utilization. In an environment of thin-enabled Veritas volumes and supported storage arrays, the amount of space used on an array will be awfully close to the amount of space used in the file systems. This is a massive win - a capacity gain of on the order of 50%-70% in an average environment!

For more on this topic, see my recent post on storage utilization

If the storage array fully supports Symantec’s API, the tools will also report physically allocated storage behind thin and thin_reclaim devices.

# vxdisk –o thin list
DANAME        DISK SIZE(Mb)        PHYS_ALLOC(Mb)       DISK GROUP TYPE
encl0_0       2000                 50 mydg              thin
encl1_0       200                  50 mydg              thinrclm
encl1_1       500                  500 mydg             thinrclm

SmartMove

SmartMove is Symantec’s new capability for online migration from “thick” to thin LUNs. It is included in Storage Foundation for Unix/Linux and Windows and works with any thin storage array, not just those that support the API. This is basically a tweak to the old storage migration support we have all known and relied on in Veritas Storage Foundation for over a decade, except that it’s smart enough to not request blocks that it won’t use. One could theoretically “SmartMove” a volume regularly to reclaim space without using the API at all, but those commands are sure a lot simpler.

Note that SmartMove speeds up migration too, even for thick volumes! When you use a SmartMove-enabled version of Storage Foundation to move a volume, it will only send the blocks that have changed over the wire. This reminds me a little of VMware’s new I/O deduplication capability talked about at VMworld, but it’s focused only on migrations, not other I/O situations.

For more on this topic, see my recent post on VMware vStorage

The Plot Thickens

So I was wrong about one item, but the other two remain true. Is Symantec’s new capability a winner? I give it a silver medal – it’s good stuff, but some issues remain.

1. My primary concern remains – thin provisioning does nothing to address the lack of storage management that is so prevalent. It enables greater utilization of capacity, but does nothing to control how that capacity is used. This isn’t a beef with Symantec’s Veritas Storage Foundation or 3PAR or HDS or EMC or anyone in the thin industry, really. Instead, it is a wake-up call to all of the storage organizations out there who have filesystems full of uncontrolled junk!
2. My second concern is the lack of capacity management. Thin provisioning is a lie, promising more capacity than is available. This might be acceptable in certain controlled circumstances like operating system or application volumes, but telling end users that they have plenty of available space is a recipe for disaster. Storage use is like air – it expands to fill all available volume. Without capacity management, your thin volumes will be “overdrawn” and your storage “account” will be bankrupt.
3. Then there is the issue of proprietary APIs versus standards. Let me say right away that I always support standards over proprietary technology. But, at the same time, given the choice between nothing and something, I’ll take the proprietary API. Thin provisioning is a good idea with poor implementation. This API helps to make it useful in the real world, and having a market leader like Symantec behind it makes it all the more relevant. I certainly hope the entire storage industry will come up with a standard thin API, and when that happens I hope Symantec will support it. Until then, at least we have something.

I will be writing more about thin provisioning in the coming weeks. Until then, I continue to applaud Symantec, 3PAR, HDS, and HP for their work in making this technology somewhat more practical. Now how about VMware, Microsoft, Sun, and the Linux guys get some thin technology going, too?

See my posts on Gestalt IT for similar enterprise IT infrastructure commentary

© sfoskett for Stephen Foskett, Pack Rat, 2008. | Symantec’s Thin API: The Plot Thickens
This post was categorized as Enterprise storage, Virtual Storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.

Hopefully, VMware's three pillars (vCloud, vClient, and VDC-OS) are a little more solid (not to mention closer) than the Three Pillars of Creation in the Eagle Nebula

VMware packed a lot into their 2008 VMworld conference, including an outline of their “three pillars” strategy, focused on vClient, vCloud, and something they are calling the Virtual Datacenter Operating System. While it is debatable if this last item really is an operating system, it’s certainly a major strategic change in messaging.

VDC-OS is divided into four “vServices” (Management, Cloud, Application, and Infrastructure), and one core Infrastructure vService is vStorage. Since my focus is enterprise storage, I thought I would take a moment to examine the current and future status of vStorage.

EMC’s Chad Sakac has taken up the challenge of communicating vStorage to the world, in a post to his blog, a pair of YouTube videos (multipathing, I/O dedupe), and (apparently) a session or two at VMworld. But I’m not sure it’s really entirely clear just what vStorage is and what this means to existing and future VMware storage developments. So let’s dive in and take a look.

vStorage = Storage vService for VMware Infrastructure

Let’s get one thing out of the way immediately: VDC-OS is not a new product – it’s a framework to organize VMware’s existing and future datacenter-targeted products like ESX. The company is sweeping away the current hodgepodge of server product elements and placing them all into a more-organized structure called VDC-OS.

As such, the whole thing is not fully baked at present – there are lots of missing elements, and these point to future products from VMware and others. I applaud the organization, and feel that this is the first really viable next-generation datacenter vision that I have seen. It accurately reflects the current reality of the corporate data center and includes a migration path to take it to a compelling new level.

VMware has a realistic approach to bringing current datacenter elements into the future

As we can see in VMware’s diagram (above), the Virtual Datacenter OS is made up of VMware Infrastructure, with application vServices resting on infrastructure vServices or the cloud. This last bit is the fundamental breakthrough that makes VDC-OS more than just slideware – if it works, applications (virtual appliances) can transparently move from local infrastructure to cloud infrastructure owned and operated by others. It’s transformative, and if they pull it off, this could usher in a new datacenter world.

vStorage is one of the core infrastructure services, along with vCompute and vNetwork. Although it’s not entirely clear at this point, vStorage presumably includes all existing VMware storage technologies as well as the new APIs for multipathing and I/O deduplication highlighted at the show. I envision a future in which vStorage is a set of APIs for everything from I/O to device management, and VMware even includes virtual storage appliances in this umbrella.

vStorage: What’s In It?

At the very least, vStorage includes the following:

• VMFS for shared storage
• Thin Provisioning support in VMware Infrastructure is apparently coming in 2009, but is also apparently incompatible with fault tolerance.
• Linked Clones is another desktop technology coming to VI 2009.
• The Site Recovery Manager API has also become part of vStorage, though this isn’t getting much press.
• VMware Consolidated Backup (VCB) will also apparently be a vStorage API.
• The existing snapshot API will also presumably included.
• The new API for Multipathing covers the old generic native multipathing (NMP) from ESX as well as EMC’s most excellent PowerPath. The latter is presumably an extra-cost option that enables lots of niftiness, as demonstrated by Chad in this video.
• Another new API claims to deduplicate I/O, reducing traffic for certain supported disk operations, as demonstrated in Chad’s second video.

What is in and what is out is still kind of up in the air. But you can see that vStorage includes most of our old favorites (VMFS, SRM, VCB), some desktop elements (thin volumes, linked clones), and some new surprises (PowerPath, I/O dedupe). There is enough meat here to separate this from traditional slideware: VDC-OS has legs!

© sfoskett for Stephen Foskett, Pack Rat, 2008. | What is VMware VDC-OS vStorage?
This post was categorized as Enterprise storage, Virtual Storage. Each of my categories has its own feed if you'd like to filter out or focus on posts like this.