IBM XIV Gen3 SSD Caching versus EMC VFCache

Have you ever noticed that sometimes two movies come out that seem eerily similar to each other, released by different studios within months or weeks of each other? My sister used to review film scripts for a living, she would read ten of them and have to pick her top three favorites, and tells me that scripts for nearly identical concepts came all the time. Here are a few of my favorite examples:

  • 1994: [Wyatt Earp] and [Tombstone] were Westerns recounting the famed gunfight at the O.K. Corral. Tombstone, Arizona is near Tucson, and the gunfight is recreated fairly often for tourists.
  • 1998: [Armageddon] and [Deep Impact] were a pair of disaster movies dealing with a large rock heading to destroy all life on earth. I was in Mazatlan, Mexico to see the latter, dubbed in Spanish as “Impacto Profundo”.
  • 1998: [A Bug's Life] and [Antz] were computer-animated tales of the struggle of one individual ant in an ant colony.
  • 2000: [Mission to Mars] and [Red Planet] were sci-fi pics exploring what a manned mission to our neighboring planet might entail.
  • 2009: [Paul Blart: Mall Cop] and [Observe and Report] were comedies dealing with challenges of security at a shopping mall.

(I think I made my point with just a few examples. A more complete list can be found on [Sam Greenspan's 11 Points website].)

This is different than copy-cat movies that are re-made or re-imagined many years later based on the previous successes of an original. Ever since my blog post [VPLEX: EMC's Latest Wheel is Round] in 2010 comparing EMC’s copy-cat product that came our seven years after IBM’s SAN Volume Controller (SVC), I’ve noticed EMC doesn’t talk about VPLEX that much anymore.

This week, IBM announced [XIV Gen3 Solid-State Drive support] and our friends over at EMC announced [VFCache SSD-based PCIe cards]. Neither of these should be a surprise to anyone who follows the IT industry, as IBM had announced its XIV Gen3 as “SSD-Ready” last year specifically for this purpose, and EMC has been touting its “Project Lightning” since last May.

Fellow blogger Chris Mellor from The Register has a series of articles to cover this, including [EMC crashes the server flash party], [NetApp slaps down Lightning with multi-card Flash flush], [HP may be going the server flash route], and [Now HDS joins the server flash party].

Fellow blogger Chuck Hollis from EMC has a blog post [VFCache means Very Fast Cache indeed] that provides additional detail. Chuck claims the VFCache is faster than popular [Fusion-IO PCIe cards] available for IBM servers. I haven’t seen the performance spec sheets, but typically SSD is four to five times slower than the DRAM cache used in the XIV Gen3. The VFCache’s SSD is probably similar in performance to the SSD supported in the IBM XIV Gen3, DS8000, DS5000, SVC, N series, and Storwize V7000 disk systems.

Nonetheless, I’ve been asked my opinions on the comparison between these two announcements, as they both deal with improving application performance through the use of Solid-State Drives as an added layer of read cache.

(FTC Disclosure: I am both a full-time employee and stockholder of the IBM Corporation. The U.S. Federal Trade Commission may consider this blog post as a paid celebrity endorsement of IBM servers and storage systems. This blog post is based on my interpretation and opinions of publicly-available information, as I have no hands-on access to any of these third-party PCIe cards. I have no financial interest in EMC, Fusion-IO, Texas Memory Systems, or any other third party vendor of PCIe cards designed to fit inside IBM servers, and I have not been paid by anyone to mention their name, brands or products on this blog post.)

The solutions are different in that IBM XIV Gen3 the SSD is “storage-side” in the external storage device, and EMC VFCache is “server-side” as a PCI Express [PCIe] card. Aside from that, both implement SSD as an additional read cache layer in front of spinning disk to boost performance. Neither is an industry first, as IBM has offered server-side SSD since 2007, and IBM and EMC have offered storage-side SSD in many of their other external storage devices. The use of SSD as read cache has already been available in IBM N series using [Performance Accelerator Module (PAM)] cards.

IBM has offered cooperative caching synergy between its servers and its storage arrays for some time now. The predecessor to today’s POWER7-based were the iSeries i5 servers that used PCI-X IOP cards with cache to connect i5/OS applications to IBM’s external disk and tape systems. To compete in this space, EMC created their own PCI-X cards to attach their own disk systems. In 2006, IBM did the right thing for our clients and fostered competition by entering in a [Landmark agreement] with EMC to [license the i5 interfaces]. Today, VIOS on IBM POWER systems allows a much broader choice of disk options for IBM i clients, including the IBM SVC, Storwize V7000 and XIV storage systems.

EMC is not the first to manufacture an SSD-based PCIe card. Last summer, my friends at Texas Memory Systems [TMS] gave away a [RAMsan-70 PCIe card] at an after-party on [Day 2 of the IBM System Storage University].

Can a little SSD really help performance? Yes! An IBM client running a [DB2 Universal Database] cluster across eight System x servers was able to replace an 800-drive EMC Symmetrix by putting eight SSD Fusion-IO cards in each server, for a total of 64 Solid-State drives, saving money and improving performance. DB2 has the Data Partitioning Feature that has multi-system DB2 configurations using a Grid-like architecture similar to how XIV is designed. Most IBM System x and BladeCenter servers support internal SSD storage options, and many offer PCIe slots for third-party SSD cards. Sadly, you can’t do this with a VFCache card, since you can have only one VFCache card in each server, the data is unprotected, and only for ephemeral data like transaction logs or other temporary data. With multiple Fusion-IO cards in an IBM server, you can configure a RAID rank across the SSD, and use it for persistent storage like DB2 databases.

Here then is my side-by-side comparison:



IBM XIV Gen3 SSD Caching

Servers supported

Selected x86-based models of Cisco UCS, Dell PowerEdge, HP ProLiant DL, and IBM xSeries and System x servers

All of these, plus any other blade or rack-optimized server currently supported by XIV Gen3, including Oracle SPARC, HP Titanium, IBM POWER systems, and even IBM System z mainframes running Linux

Operating System support

Linux RHEL 5.6 and 5.7, VMware vSphere 4.1 and 5.0, and Windows 2008 x64 and R2.

All of these, plus all the other operating systems supported by XIV Gen3, including AIX, IBM i, Solaris, HP-UX, and Mac OS X

Protocol support



Vendor-supplied driver required on the server

Yes, the VFCache driver must be installed to use this feature.

No, IBM XIV Gen3 uses native OS-based multi-pathing drivers.

External disk storage systems required

None, it appears the VFCache has no direct interaction with the back-end disk array, so in theory the benefits are the same whether you use this VFCache card in front of EMC storage or IBM storage

XIV Gen3 is required, as the SSD slots are not available on older models of IBM XIV.

Shared disk support

No, VFCache has to be disabled and removed for vMotion to take place.

Yes! XIV Gen3 SSD caching shared disk supports VMware vMotion and Live Partition Mobility.

Support for multiple servers


An advantage of the XIV Gen3 SSD caching approach is that the cache can be dynamically allocated to the busiest data from any server or servers.

Support for active/active server clusters



Aware of changes made to back-end disk

No, it appears the VFCache has no direct interaction with the back-end disk array, so any changes to the data on the box itself are not communicated back to the VFCache card itself to invalidate the cache contents.


Sequential-access detection

None identified. However, VFCache only caches blocks 64KB or smaller, so any sequential processing with larger blocks will bypass the VFCache.

Yes! XIV algorithms detect sequential access and avoid polluting the SSD with these blocks of data.

Number of SSD supported

One, which seems odd as IBM supports multiple Fusion-IO cards for its servers. However, this is not really a single point of failure (SPOF) as an application experiencing a VFCache failure merely drops down to external disk array speed, no data is lost since it is only read cache.

6 to 15 (one per XIV module) for high availability.

Pin data in SSD cache

Yes, using split-card mode, you can designate a portion of the 300GB to serve as Direct-attached storage (DAS). All data written to the DAS portion will be kept in SSD. However, since only one card is supported per server and the data is unprotected, this should only be used for ephemeral data like logs and temp files.

No, there is no option to designate an XIV Gen3 volume to be SSD-only. Consider using Fusion-IO PCIe card as a DAS alternative, or another IBM storage system for that requirement.


Not identified


Pre-sales Estimating tools

None identified

Yes! CDF and Disk Magic tools are available to help cost-justify the purchase of SSD based on workload performance analysis.

IBM has the advantage that it designs and manufactures both servers and storage, and can design optimal solutions for our clients in that regard.

technorati tags: IBM, XIV, Gen3, SSD, cache, EMC, VFCache, Project Lightning, SVC, Solid State Drives, Fusion-IO, Texas Memory Systems, RAMSan, System+x, POWER systems, VIOS, DRAM, VMware, Vmotion, Live Partition Mobility, AIX, IBM i, PCIe, PCI-X

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