Tag Archives: vmware

EMC VPLEX enables the private cloud.. But what is a “private cloud”?

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Buzzword Much?

If you have seen any of EMC’s marketing for EMC World, or you are attending EMC World in Boston this week, you no doubt noticed a ton of talk about the “Private Cloud”.  There has been a lot more talk from vendors as of late about the “cloud” and “cloud computing” and you may be reminded about how every few years the word “cloud” is shouted out by vendors of all kinds and how inevitably the talk quiets and nothing is really different.  So is it different this time?  I think so.

What is a Cloud?

In the context of IT, there are examples of clouds already.  The Internet and public telephone system are two examples of clouds.  Facebook, Flickr, and Salesforce are examples of clouds as well.  The common theme is that each of these examples provides some sort of service to the end user without requiring the end user to purchase or build any infrastructure to support it.  You can plug a phone into a wall and immediately call nearly anyone in the world.  Cloud is a fancy word (or buzzword) for providing something “as-a-service”.  Salesforce.com is software-as-a-service (SaaS).

So what is the Private Cloud?  

In the context of enterprise datacenters, the focus of EMC’s vision, the Private Cloud is Infrastructure-as-a-service (IaaS) and it enables corporate IT to transition from a necessary expense, to a profit center within the business, providing IT-as-a-Service to the rest of the business.  It decouples infrastructure from applications providing unprecedented levels of scalability, availability, and flexibility at lower cost.

What if…
a.) your corporate applications could run from anywhere, and users had access from anywhere?
b.) you could relocate your applications from anywhere to anywhere else, at any time, without disruption to your users.
c.) you could replace any piece of physical hardware in your infrastructure without impacting your applications.

Sounds too good to be true right? Maybe not…

This week, EMC announced a completely new product called VPLEX.  VPLEX has the ability to take your existing storage arrays and pool them into a cooperative pool of storage for hosts and applications.  It then allows you to move application data within and across those arrays as needed without disrupting the application or users.  If you are familiar with EMC’s Invista, IBM’s SVC, or Hitachi’s USP-V products you may be thinking that VPLEX is just another storage virtualization product.  But I assure you it’s different.  VPLEX virtualizes storage within the datacenter similar to how the above products can, but VPLEX can ALSO combine storage across multiple datacenters and allow an application to run from any of them or all of them, simultaneously, through the power of Federation.

Active/Active Datacenters

With VPLEX Federation, you can move a virtual machine and all of its data from datacenter A to datacenter B in a matter of minutes without user disruption; or hundreds of VMs, or thousands of VMs.  You can run the same application in both locations, sharing a single dataset.  Armed with EMC VPLEX and VMWare vSphere, you can upgrade, replace, and reconfigure any part of your infrastructure (storage, servers, network, power distribution, etc) without ever having to take your applications offline.  How’s that for availability?

The ability to create a virtual infrastructure from the storage layer through to the server layer and host any application on that infrastructure is the key to creating providing Infrastructure-as-a-Service, building the Private Cloud, and provisioning IT-as-a-Service within your organization.  Imagine running the IT department as a business within the business and actually showing financial value to the business.

There is a lot more to this concept but I wanted to at least bring some context around “cloud” as well as EMC’s new VPLEX product.  There will be more to come on this topic.

Chuck Hollis wrote about VPLEX as a new Storage Platform today, and VirtualGeek called it a Virtual Machine teleporter in his quite detailed write up of this new technology.  The key is to step back with an open mind and think about how application design and disaster recovery planning could be approached in entirely new ways when the data is no longer confined to a particular physical location.

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NetApp and EMC: Exchange 2007 Replication

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Exchange Replication

Building on the redundant storage project, we also wanted to replicate Exchange to a remote datacenter for disaster recovery purposes.  We’ve been using EMC CLARiiON MirrorView/A and Replication Manager for various applications up to now and decided we’d use NetApp/SnapMirror for Exchange to leverage the additional hardware as well as a way to evaluate NetApp’s replication functionality vs EMC’s.

On EMC Clariion storage, there are a couple choices for replicating applications like Exchange.
1.) Use MirrorView/Async with Consistency Groups to replicate Exchange databases in a crash-consistent state.
2.) Use EMC Replication Manager with Snapview snapshots and SANCopy/Incremental to update the remote site copy.

Similar to EMC’s Replication Manager, NetApp has SnapManager for various applications, which coordinates snapshots, and replica updates on a NetApp filer.

Whether using EMC RM or NetApp SM, software must be installed on all nodes in the Exchange cluster to quiesce the databases and initiate updates.  The advantage of Consistency groups with MirrorView is that no software needs to be installed in the host; all work is performed within the storage array.  The advantage of RM and SM/E is that database consistency is verified on each update and the software can coordinate restoring data to the same or alternate servers, which must be done manually if using MirrorView.

NetApp doesn’t support consistent snapshots across multiple volumes so the only option on a Filer is to use SnapManager for Exchange to coordinate snapshots and SnapMirror updates.

Our first attempt configuring SnapManager for Exchange actually failed when we ran into a compatibility issue with SnapDrive.  SnapManager depends on SnapDrive for mapping LUNs between the host and filer, and to communicate with the filer to create snapshots, etc.  We’d discussed our environment with NetApp and IBM ahead of time, specifically that we have Exchange CCR running on VMWare, with FiberChannel LUNs and everyone agreed that SnapDrive supports VMWare, Exchange, Microsoft Clustering, and VMWare Raw Devices.  It turns out that SnapDrive 6 DOES support all of this, but not all at the same time.  Specifically, MSCS clustering is not supported with FC Raw Devices on VMWare.  In comparison, EMC’s Replication Manager has supported this configuration for quite a while.  After further discussion NetApp confirmed that our environment was not supported in the current version of SnapDrive (6.0.2) and that SnapDrive 6.2, which was still in Beta, would resolve the issue.

Fast forward a couple months, SnapDrive 6.2 has been released and it does indeed support our environment so we’ve finally installed and configured SnapDrive and SnapManager.  We’ve dedicated the EMC side of the Exchange environment for the active nodes and the IBM for the passive nodes.  SnapManager snapshots the passive node databases, mounts them to run database verification, then updates the remote mirror using SnapMirror.

While SnapManager does do exactly what we need it to do, my experience with it hasn’t been great so far…  First, SnapManager relies on Windows Task Scheduler to run scheduled jobs, which has been causing issues.  The job will run on its schedule for a day, then stop after which the task must be edited to make it run again.  This happens in the lab and on both of our production Exchange clusters.  I also found a blog post about this same issue from someone else.

The other issue right now is that database verification takes a long time, due to the slow speed of ESEUTIL itself.  A single update on one node takes about 4 hours (for about 1TB of Exchange data) so we haven’t been able to achieve our goal of a 2-hour replication RPO.  IBM will be onsite next week to review our status and discuss any options.  An update on this will follow once we find a solution to both issues.  In the meantime I will post a comparison of replication tools between EMC and NetApp soon.

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Capacity vs Performance: Thin Provisioning-Reclaiming Free Space

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A comment about HDS’s Zero Page Reclaim on one of my previous posts got me thinking about the effectiveness of thin provisioning in general.  In that previous post, I talked about the trade-offs between increased storage utilization through the use of thin-provisioning and the potential performance problems associated with it.

There are intrinsic benefits that come with the use of thin provisioning.  First, new storage can be provisioned for applications without nearly as much planning.  Next, application owners get what they want, while storage admins can show they are utilizing the storage systems effectively.  Also, rather than managing the growth of data in individual applications, storage admins are able to manage the growth of data across the enterprise as a whole.

Thin provisioning can also provide performance benefits…  For example, consider a set of virtual Windows servers running across several LUNs contained in the same RAID group.  Each Windows VM stores its OS files in the first few GB of their respective VMDK files.  Each VMDK file is stored in order in each LUN, with some free space at the end.  In essence, we have a whole bunch of OS sections separated by gaps of no data.  If all VMs were booting at approximately the same time, the disk heads would have to move continuously across the entire disk, increasing disk latency.

Now take the same disks, configured as a thin pool, and create the same LUNs (as thin LUNs) and the same VMs.  Because thin-provisioning in general only writes data to the physical disks as it’s being written by the application, starting from the beginning of the disk, all of those Windows VMs’ OS files will be placed at the beginning of the disks.  This increased data locality will reduce IO latency across all of the VMs.  The effect is probably minor, but reduced disk latency translates to possibly higher IOPS from the same set of physical disks.  And the only change is the use of thin-provisioning.

So back to HDS Zero Page Reclaim.  The biggest problem with thin provisioning is that it doesn’t stay thin for long.  Windows NTFS, for example, is particularly NOT thin-friendly since it favors previously untouched disk space for new writes rather than overwriting deleted files.  This activity eventually causes a thin-LUN to grow to it’s maximum size over time, even though the actual amount of data stored in the LUN may not change.  And Windows isn’t the only one with the problem.  This means that thin provisioning may make provisioning easier, or possibly improve IO latency, but it might not actually save you any money on disk.  This is where HDS’s Zero Page Reclaim can help.  Hitachi’s Dynamic Provisioning (with ZPR) can scan a LUN for sections where all the bytes are zero and reclaim that space for other thin LUNs.  This is particularly useful for converting thick LUNs into thin LUNs.  But, it can only see blocks of zeros, and so it won’t necessarily see space freed up by deleting files.  Hitachi’s own documentation points out that many file systems are not-thin friendly, and ZPR won’t help with long-term growth of thin LUNs caused by actively writing and then deleting data.

Although there are ways to script the writing of zeros to free space on a server so that ZPI can reclaim that space, you would need to run that script on all of your servers, requiring a unique tool for each operating system in your environment.  The script would also have to run periodically, since the file system will grow again afterward.

NetApp’s SnapDrive tool for Windows can scan an NTFS file system, detect deleted files, then report the associated blocks back to the Filer to be added back to the aggregate for use by other volumes/LUNs.  The Space Reclamation scan can be run as needed, and I believe it can be scheduled; but, it appears to be Windows only.  Again, this will have to be done periodically.

But what if you could solve the problem across most or all of your systems, regardless of operating system, regardless of application, with real-time reclamation?  And what if you could simultaneously solve other problems?  Enter Symantec’s Storage Foundation with Thin-Reclamation API.  Storage Foundation consists of VxFS, VxVM, DMP, and some other tools that together provide dynamic grow/shrink, snapshots, replication, thin-friendly volume usage, and dynamic SAN multipathing across multiple operating systems.  Storage Foundation’s Thin-Reclamation API is to thin-provisioning what OST is to Backup Deduplication.  Storage vendors can now add near-real-time zero page reclaim for customers that are willing to deploy VxFS/VxVM on their servers.  For EMC customers, DMP can replace PowerPath, thereby offsetting the cost.

As far as I know, 3PAR is the first and only storage vendor to write to Symantec’s thin-API, which means they now have the most dynamic, non-disruptive, zero-page-reclaim feature set on the market.  As a storage engineer myself, I have often wondered if VxVM/VxFS could make management of application data storage in our diverse environment easier and more dynamic.  Adding Thin-Reclamation to the mix makes it even more attractive.  I’d like to see more storage vendors follow 3PAR’s lead and write to Symantec’s API.  I’d also like to see Symantec open up both OST and the Thin-Reclamation API for others to use, but I doubt that will happen.

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NetApp and EMC: Startup and First Impressions

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In the last post, I talked about a project I am involved in right now to deploy NetApp storage alongside EMC for SAN and NAS.  Today, I’m going to talk about my first impressions of the NetApp during deployment and initial configuration.

First Impressions

I’m going to be pretty blunt — I have been working with EMC hardware and software for a while now, and I’m generally happy with the usability of their GUIs.  Over that time, I’ve used several major revisions of Navisphere Manager and Celerra Manager, and even more minor revisions, and I’ve never actually found a UI bug.  To be clear, EMC, IBM, NetApp, HDS, and every other vendor have bugs in their software, and they all do what they can to find and fix them quickly, but I just haven’t personally seen one in the EMC UIs despite using every feature offered by those systems. (I have come across bugs in the firmware)

Contrast that with the first day using the new NetApp, running the latest 7.3.1.1L1 code, where we discovered a UI problem in the first 10 minutes.  When attempting to add disks to an aggregate in FilerView, we could not select FC disk to add.  We could, however, add SATA disk to the FC aggregate.  The only way to get around the issue was to use the CLI via SSH.  As I mentioned in my previous post, our NetApp is actually an IBM nSeries, and IBM claims they perform additional QC before their customers get new NetApp code.

Shortly after that, we found a second UI issue in FilerView.  When creating a new Initiator group, FilerView populates the initiator list with the WWNs that have logged in to it.  Auto-populating is nice but the problem is that FilerView was incorrectly parsing the WWN of the server HBAs and populating the list with NodeWWNs rather than PortWWNs.  We spent several hours trying to figure out why the ESX servers didn’t see any LUNs before we realized that the WWNs in the Initiator group were incorrect.  Editing the 2nd digit on each one fixed the problem.

I find it interesting that these issues, which seemed easy to discover, made it through the QC process of two organizations.  ONTap 7.3.2RC1 is available now, but I don’t know if these issues were addressed.

Manageability

As far as FilerView goes, it is generally easy to use once you know how NetApp systems are provisioned.  The biggest drawback in an HA-Filer setup is the fact you have to open FilerView separately for each Filer and configure each one as a separate storage system.  Two HA-Filer pairs? Four FilerView windows.  If you include the initial launch page that comes up before you get to the actual FilerView window, you double the number of browser windows open to manage your systems.  NetApp likes to mention that they have unified management for NAS and SAN where EMC has two separate platforms, each with their own management tools. EMC treats the two storage processors (SPs) in a Clariion in a much more unified manner, and provisioning is done against the entire Clariion, not per SP.  Further, Navisphere can manage many Clariions in the same UI.  Celerra Manager acts similarly for EMC NAS.  Six of one, half a dozen of the other some say, except that I find that I generally provision NAS storage and SAN storage at different times, and I’d rather have all of the controllers/filers in the same window than NAS and SAN in the same window.  Just my preference.

I should mention, NetApp recently released System Manager 1.0 as a free download.  This new admin tool does present all of the controllers in one view and may end up being a much better tool than FilerView.  For now, it’s missing too many features to be used 100% of the time and it’s Windows only since it’s based on MMC.  Which brings me to my other problem with managing the NetApp.  Neither FilerView nor System Manager can actually do everything you might need to do, and that means you end up in the CLI, FREQUENTLY.  I’m comfortable with CLIs and they are extremely powerful for troubleshooting problems, and especially for scripting batch changes, but I don’t like to be forced into the CLI for general administration.  GUI based management helps prevent possibly crippling typos and can make visualizing your environment easier.  During deployment, we kept going back and forth between FilerView and CLI to configure different things.  Further, since we were using MultiStore (vFilers) for CIFS shares and disaster recovery, we were stuck in the CLI almost entirely because System Manager can’t even see vFilers, and FilerView can only create them and attach volumes.

Had I not been managing Celerra and Clariion for so long, I probably wouldn’t have noticed the above problems.  After several years of configuring CIFS, NFS, iSCSI, Virtual DataMovers, IP Interfaces, Snapshots, Replication, and DR Failover, etc. on Celerra, as well as literally thousands of LUNs for hundreds of servers on Clariion, I don’t recall EVER being forced to use the CLI.  CelerraCLI and NaviCLI are very powerful, and I have written many scripts leveraging them, and I’ll use CLI when troubleshooting an issue.  But for every single feature I’ve ever used on the Celerra or Clarrion, I was able to completely configure from start to finish using the GUI.  Installing a Celerra from scratch even uses a GUI based installation wizard.  Comparing Clariion Storage Groups with NetApp Initiator groups and LUN maps isn’t even fair.  For MS Exchange, I mapped about 50 LUNs to the ESX cluster, which took about 30 minutes in FilerView.  On the Clariion, the same operation is done by just editing the Storage Group and checking each LUN, taking only a couple minutes for the entire process.

Now, all of the above commentary has to do with the management tools, UIs, and to some degree personal preferences, and does not have any bearing on the equipment or underlying functionality.  There are, of course, optional management tools like Operations Manager, Provisioning Manager, and Protection Manager available from NetApp, just as there is Control Center from EMC (which incidentally can monitor the NetApp) or Command Central from Symantec.  Depending on your overall needs, you may want to look at optional management tools; or, FilerView may be perfectly fine.

In the next post,  I’ll get into more specifics about how the Exchange 2007 CCR cluster turned out in this new environment, along with some notes on making CCR truly redundant.  I’ve also been working on the NAS side of the project, so I’ll also post about that some time soon.

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Backup Everything – The datacenter done fast!

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I support a very diverse environment with a mix of Windows, Netware, Linux, Solaris, and Mac clients running on standard servers as well as VMWare ESX, plus two different brands of NAS, a few iSeries systems, and an Apple XSAN thrown in for good measure.  We have hundreds of applications running on these systems including SQL, Oracle, MySQL, Sharepoint, Documentum, and Agile.  These applications are mostly contained in our primary datacenter but we also have a few remote datacenters for specific applications and for disaster recovery as well as a couple remote business offices.

Recently I’ve been working on a project to replace our existing backup application with a new one.  We were experiencing extremely long backup windows, low throughput per client, and high backup failure rates with our existing solution and it was time to make a change of some kind.  The goal was to protect all of our systems regardless of their location with both an onsite backup in our primary datacenter and an offsite copy for disaster recovery purposes.  Additionally we wanted to use little or no tape.  After research, lots of vendor meetings, a consulting engagement, and lengthy debate we chose Symantec NetBackup with Symantec NetBackup PureDisk and DataDomain.  This combination was chosen for several reasons which will become clearer below.

For those of you who are not familiar with these products here’s a brief description..

Symantec Netbackup is a traditional backup solution that is designed to move data from many clients, as fast as possible, to disk or tape.  It is similar to EMC Networker, Symantec BackupExec, and any number of other backup products.  NetBackup supports a wide variety of clients, NAS devices, applications (SQL, Exchange, etc), as well as tape libraries and disk storage for the backed up data.  Since it simply copies all of the data that resides on the client directly to the backup server it is not particularly tuned for backing up remote offices across the WAN but it can easily flood a local LAN during a backup.

Symantec NetBackup PureDisk is currently a separate solution from the base NetBackup product; it is designed specifically for backing up data over the WAN.  Puredisk is a “source-dedupe” solution and is very similar in function to EMC’s Avamar product with which I have a long standing love affair. PureDisk performs an incremental-forever style of backup where only the data that changed since the last backup is copied to the backup server.  It then uses deduplication technology to reduce the resulting backup dataset down to an even smaller size before it gets copied across the network.  The data is collected and stored (in it’s deduplicated form) on the backup server.  With this design PureDisk saves network bandwidth as well as disk space on the backup server making it ideal for backups across the WAN, VPN, etc.  Symantec’s goal is to merge PureDisk into NetBackup as a single solution at some point probably next year.  PureDisk backup servers can replicate backed up data to other PureDisk backup servers in de-duplicated form for redundancy across sites. The downside to PureDisk is that raw throughput on a PureDisk backup server is not high enough for datacenter use and client support is more limited than the standard NetBackup product.

DataDomain (now part of EMC) has been making it’s DDR products for a while now and has been very successful (prompting the recent bidding war between NetApp and EMC to purchase the company).  DataDomain appliances are “target-dedupe” devices that are designed to replace tape libraries in traditional backup environments, like Netbackup.  The DDR appliance presents itself as a VTL (virtual tape library) via SAN, a CIFS(Windows) file server, and/or a NFS(UNIX) file server making it compatible with pretty much any type of backup system.  DataDomain also supports Symantec’s OpenSTorage (OST) API which is available in Netbackup 6.5.  The DDR system receives all of the data that Netbackup copies from backup clients, deduplicates the data in real-time, then stores it on it’s own internal disk.  Because the DDR is purpose built and has fast processors it can process data at relatively high throughput rates.  For example, a single DD690 model is rated at 2.7TB/hour (about 6gbps) when using OST.  The deduplication in a DDR provides disk-space savings but does not reduce the amount of data copied from backup clients.  DDRs can also replicate data (in deduplicated form) to other DDRs across the LAN or WAN, great for offsite backups.

For an explanation of de-duplication, check out my prior post on the topic..

Two of the challenges we faced when designing the final solution had to do with the cost per TB of DataDomain disk and the slightly limited client OS support of PureDisk.  But we had a clean slate to work from–there was no interest in utilizing any of the existing backup infrastructure aside from the two IBM tape libraries we had.  We were not required to use the libraries but we wouldn’t be buying new ones if we planned on using tape as part of the new solution.

For the primary datacenter we deployed NetBackup Master and Media servers, a DataDomain DD690, and connected them to each other with Cisco 4900M 10gbps switches.  We deployed a warm-standby master server plus a media server and another DD690 in our DR datacenter but did not use 10gbs there due to the additonal cost.

With this set up we covered all of the clients in our primary datacenter.  Systems that have large amounts of data (like Microsoft Exchange, SAS Financials, etc) were connected directly to the 4900M switches (via 1gbps connections).  Aggregate throughput of the backups during a typical night averages 400-500MB/sec with all of the data going to the DataDomain.  The Exchange server’s flood their network links pushing over 100MB/sec per server when backing up the email databases.  We currently back up 9TB of data per night with 3 media servers and a single DDR in about 5 hours.  Our primary bottlenecks are with the VCB Proxy server (we need more of them) and the aging datacenter core network having an aggregate throughput of a barely more than 1gbps.

But what about those remote sites?  What does OST really add?  How do you tackle the NAS backups without resorting to tape?  All that and more is coming up soon…

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Capacity vs. Performance : Thin Provisioning

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In my previous post, where I discussed the problem of unusable (or slack) disk space on a SAN, I promised a follow-up with techniques on how to increase storage utilization.  I realized that I should discuss some related technologies first and then follow that up with how to put it all together.  So today I start by talking about Thin Provisioning.  I will then follow up with an explanation of De-Duplication and finally talk about how to use multiple technologies together to get the most use out of your storage.

So what is Thin Provisioning?  It is a technology that allows you to create LUNs or Volumes on a storage device such that the LUN/Volume(s) appear to the host or client to be larger than they actually are.   In general, NAS clients and SAN attached hosts see “Thin Provisioned” LUNs just as they see any other LUN but the actual amount of disk space used on the storage device can be significantly smaller than the provisioned size.  How does this help increase storage utilization?  Well, with thin provisioning you provide applications with exactly the storage they want and/or need but you don’t have to purchase all of the disk capacity up front.

Let’s start with a comparison of using standard LUNs vs thin LUNs with a theoretical application set:

Say we have 3 servers, each running Windows Server.  The operating system partition is on local disk and application data drives are on SAN.  Each server runs an application that collects and stores data over time and the application owner expects that over the next year or so the data will grow to 1TB on each server.  In this particular case we also know that the application’s performance requirements are relatively low.

With traditional provisioning we might create 3 LUNs that are 1TB each and present them to the servers.  This provides the application with room for the expected growth.  Using 300GB FC disks we can carve out three 4+1 RAID5 sets, create one LUN in each and it would work fine.  Alternatively we could use wide striping (ie: a MetaLUN on EMC Clariion) and put all three LUNs on the same 15 disks.  Either way we’ve just burned 15 disks on the storage array based on uncertain future requirements.  If we were stingier with storage we could create smaller LUNs (500GB for example) and use LUN expansion technology to increase the size when the application data fills the disk to that capacity.

In the Thin Provisioning world we still create three 1TB LUNs but they would start out by taking no space.  The pool of disk that the LUNs get provisioned from doesn’t even need to have 3TB of capacity.  As the application data grows over the next 12 months or longer the pool size only needs to grow to accommodate the actual amount of data stored.  Depending on the storage array, we can add disks to the pool one at a time.  So on day one we start with 3 disks in the pool, and then add additional disks one by one throughout the year.  We can then create additional LUNs for other applications without adding disks.  As we add disks to the pool, we expand the capacity available for all of the LUNs to grow (up to each LUN’s maximum size) and we increase performance for ALL of the LUNs in the pool since we are adding spindles.  The real-world benefits come as we consolidate numerous LUNs into a single disk pool.

The nice thing about this approach is that we stop managing the size of individual LUNs and just manage the underlying disk pool as a whole.   And the cost-per-GB for SAN disk constantly goes down so we can spend only what we have to today, and when we add more later it will likely be a little cheaper.  Disk capacity utilization will be much higher in a thin model compared with the traditional/thick model.

The story gets even better in a virtual server environment such as with MS Hyper-V or VMWare ESX.  First, the virtual server OS drives are on the SAN in addition to the application data, and there can be multiple virtual disks on the same LUN.  Whether physical or virtual, we need to maintain some free space in the disks to keep applications running, plus with virtual systems we need some free space on the LUN for features of the virtualization technology like snapshots.  The net effect is that in a virtualized environment, disk utilization never gets much above 50% when slack space at both the virtual layer and inside the virtual servers is considered.  With thin provisioning we could potentially store twice the number of virtual servers on the same physical disks.

There are caveats of course.  Maintaining performance is the primary concern.  Whether used in a thick LUN or thin LUN, each disk has a specific amount of performance.   Thin provisioning has no effect on the amount of IOPS or bandwidth the application requires nor the amount of IOPS the physical disk can handle.  So even if thin provisioning saves 50% disk space in your environment, you may not be able to use all of that reclaimed space before running into performance bottlenecks.  If the storage array has QOS features (ie: EMC Clariion NQM) it is possible to prioritize the more important applications in your disk pool to maintain performance where it matters.

Other problems that you may encounter have to do with interoperability.  For starters, some applications are not “thin-friendly”; ie: they write data in such a way as to negate any benefit that thin provisioning provides.  Also, while many storage arrays support thin provisioning, each has different rules about the use of thin LUNs.  For example, in some scenarios you can’t replicate thin LUNs using native array tools.  It pays to do your homework before choosing a new storage array or implementing thin provisioning.

I didn’t cover thin provisioning in NAS environments directly but the feature works in the same manner.  Thin volumes are provisioned from pools of storage and users/clients see a large amount of available disk space even if the disk pool itself is very small.  Since NAS is traditionally used for user home directories and departmental shares, absolute performance is usually not as much of a concern so thin provisioning is much easier to implement and in many cases is the default behavior or simply a check box on NAS appliances like EMC Celerra or NetApp FAS.

Thin provisioning is a powerful technology when used where it makes sense.  In my next post I’ll explain de-duplication technology and then talk about how these technologies can be used together plus some workarounds for the caveats that I’ve mentioned.

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