The reverse wars – DAS vs NAS vs SAN

It has been quite an interesting 2 decades.

In the beginning (starting in the early to mid-90s), SAN (Storage Area Network) was the dominant architecture. DAS (Direct Attached Storage) was on the wane as the channel-like throughput of Fibre Channel protocol coupled by the million-device addressing of FC obliterated parallel SCSI, which was only able to handle 16 devices and throughput up to 80 (later on 160 and 320) MB/sec.

NAS, defined by CIFS/SMB and NFS protocols – was happily chugging along the 100 Mbit/sec network, and occasionally getting sucked into the arguments about why SAN was better than NAS. I was already heavily dipped into NFS, because I was pretty much a SunOS/Solaris bigot back then.

When I joined NetApp in Malaysia in 2000, that NAS-SAN wars were going on, waiting for me. NetApp (or Network Appliance as it was known then) was trying to grow beyond its dot-com roots, into the enterprise space and guys like EMC and HDS were frequently trying to put NetApp down.

It’s a toy”  was the most common jibe I got in regular engagements until EMC suddenly decided to attack Network Appliance directly with their EMC CLARiiON IP4700. EMC guys would fondly remember this as the “NetApp killer“. Continue reading

Supercharging Ethernet … with a PAUSE

It’s been a while since I wrote. I had just finished a 2-week stint in Melbourne, conducting 2 Data ONTAP classes and had a blast.

But after almost 3 1/2 months of doing little except teaching NetApp classes, the stint is ending. I wanted it that way, to take a break and also to take on a new challenge. I will be taking on a job with Hitachi Data Systems, going back to the industry that I have termed the “Wild, wild west”. After a 4 1/2-year hiatus, I think that industry still behaves the way it is .. brash, exclusive, rich! The oligarchy of the oilmen are still laughing their way to the banks. And it will be my job to sell storage (and cloud) solutions to them.

In my Netapp (and EMC) engagements in the past 6 months, I have seen the greater adoption of iSCSI over Fibre Channel, and many has predicted that 10Gigabit Ethernet will be the infliction point where iSCSI can finally stand shoulder-to-shoulder with Fibre Channel. After all, 10 Gigabit/sec is definitely faster than 8 Gigabit/sec Fibre Channel, right? WRONG! (I am perfectly aware there is a 16 Gigabit/sec Fibre Channel, but can’t you see I am trying to start an argument here?)

Delivering SCSI data load over iSCSI on 10 Gigabit/sec Ethernet does not necessarily mean that it would be faster than delivering the same payload over 8 Gigabit/sec Fibre Channel. This statement can be viewed in many different ways and hence the favourite IT reply would be … “It depends“.

I would leave this performance argument for another day but today we are going to talk about some of the key additions to supercharge 10 Gigabit Ethernet for data delivery in storage networking capacity. In addition, 10 Gigabit Ethernet is the primary transport for Fibre Channel over Ethernet (FCoE) and it is absolutely critical that 10 Gigabit Ethernet must be close to as reliable as Fibre Channel for data delivery in a storage network.

Ethernet is a non-deterministic protocol, and therefore, its delivery result is dependent on many factors. Likewise 10 Gigabit Ethernet has inherited part of that feature. The delivery of data over Ethernet can be lossy, i.e. packets can get lost and the upper layer application protocols will have to respond to detecte the dropped packets and to ensure lost packets are redelivered to complete the consignment. But delivering data in a storage network cannot be lossy and in most cases of SANs, the requirement is to have the data arrive in the sequence they were delivered. The SAN fabric (especially with the common services of Layer 3 of the FC protocol stack) and the deterministic nature of Fibre Channel protocol were the reasons many has relied on Fibre Channel SAN technology for more than a decade. How can 10 Gigabit Ethernet respond?

Continue reading

The beginning of the end of FCoE

Never bet against Ethernet!

I am sure many IT experts and practitioners would agree. In the past 30 years or so, Ethernet has fought and won against many so-called would be “Ethernet killers”. The one that stood out for me was ATM (Asynchronous Transfer Mode) because in my past job, I implemented NFS over ATM, running in LANE (LAN Emulation) mode in a NetApp filer setup in Sarawak Shell.

That was more than 10 years ago. And 10 years ago, ATM was hot technology. It was touted as the next generation network technology and supposed to unify the voice, data and network together. ATM also had better framing and QOS (Quality-of-Service) control and offers several modes of traffic shaping and policies. And today, ATM is reduced to a niche telecommunication protocol, and do not participate much in the LAN technology space.

That was the networking space. The storage networking space is dominated by Fibre Channel for almost 15 years. Fibre Channel is a serial technology that replaced the channel-based technology of SCSI in the enterprise. And Fibre Channel has also grown leaps and bounds, dominating the SAN (Storage Area Network) landscape with speeds up to 16Gbit/sec today.

When the networking world and storage networking world collided (I mean combined) with Fibre Channel over Ethernet (FCoE) technology some years back, one has got to give some time soon. Yup, FCoE was really hot 2 years ago, but where is it today? Is Cisco still singing about FCoE like it used to? What about the other storage vendors that used to have at least 1 FCoE slide in their product presentation?

Welcome to the world of IT hypes! FCoE benefits? Ability to carry LAN and SAN traffic with one piece of wire. 10 Gigabit-style, baby!

Continue reading

Linking Apple to SAN

Serendipity is what I would describe this encounter. I was introduced to Promise Technology Channel Sales Director early this week. When I saw his face, I realized that I already knew him, a Malaysian who previously worked at EMC in Taiwan, but has been residing in that country for many years. We laughed and joked like old buddies and hence, the story begins …

I have known of Promise through its popular VTrak storage, which many Apple users here ignorantly associate as an Apple product. Here it is, appearing on Apple’s website:

Yes, that’s the 3rd picture from your left.

Another very strong Apple product from Promise Technology is Pegasus, a storage line of direct-attached storage (DAS) sporting the Thunderbolt, a very fast interface that connects peripherals to Macs through its Mini DisplayPort. I found this strange having a graphics display port being used to connect to a storage device, but as I looked deeper into Thunderbolt, I found that the technology was meant to extend the PCIe bus with the DisplayPort into a conduit that delivers high throughput serially. Impressive!

The picture below shows the Thunderbolt link connections, in which
Intel will provide two types of Thunderbolt controllers, a 2 port type and a 1 port type.

But Thunderbolt is not a network-based technology. It is channel-based, and hence, connecting to a Fibre Channel SAN is like mixing oil with water. Apple is not known for accessing storage through Fibre Channel, and since Apple products do not have a Fibre Channel interface, Promise Technology has come up with Thunderbolt to Fibre Channel converter. They call it SANLink. And the picture below shows how it is done:

The SANLink can also be daisy-chained. In the example below, the Pegasus DAS is daisy-chained to a SANLink which then extends and expands its capacity from the Fibre Channel connected VTrak Ex30 or Ex10.

The connectivity can be 8Gbps for the VTrak Ex30, and 4Gbps for the Ex10, and it has been validated to work with MacOS X, Final Cut Studio and Apple’s Xsan.

This is targeted to the Apple’s presence in the video editing and video production environment. I have 1 customer using our storage for their Apple file sharing purpose, and I realized that these guys work in isolation most of the time. They are like a sheep-shearing house, taking one job, work on it a bit and then pass it on to another colleague for the next stage in the video production process. Sharing is clearly not well known in this type of environment. And Promise wants to change that by opening to those hermit-like video editors and producers to share and collaborate in their work.

I don’t know much about other vendors besides Apple that pushes the Thunderbolt technology. It is very high performance interface, capable of delivering 20Gbps but I am afraid that Thunderbolt may suffer from the Apple-only syndrome.

Apple tend to be very cutting-edge when it comes to most technologies that go into their products. That makes Apple high risk takers, and that puts Thunderbolt into that risky category when if Apple fails, Thunderbolt fails. So far, I have not seen Thunderbolt spreading like wildfire, but opening Apple to SAN, both iSCSI and Fibre Channel, is good. It is time Apple embrace more of the storage networking technologies and standards out there, rather than being steadfast with their proprietary implementation of storage. Apple File Protocol (AFP) and Thunderbolt (for now) comes to mind. It is good to be stubborn but …

NFS deserves more credit from guys doing virtualization

I was at the RedHat Forum last week when I chanced upon a conversation between an attendee and one of the ECS engineers. The conversation went like this

Attendee: Is the RHEV running on SAN or NAS?

ECS Engineer: Oh, for this demo, it is running NFS but in production, you should run iSCSI or Fibre Channel. NFS is only for labs only, not good for production.

Attendee: I see … (and he went off)

I was standing next to them munching my mini-pizza and in my mind, “Oh, come on, NFS is better than that!”

NAS has always played a smaller brother to SAN but usually for the wrong reasons. Perhaps it is the perception that NAS is low-end and not good enough for high-end production systems. However, this is very wrong because NAS has been growing at a faster rate than Fibre Channel, and at the same time Fibre Channel growth has been tapering and possibly on the wane. And I have always said that NAS is a better suited protocol when it comes to unstructured data and files because the NAS protocol is the new storage networking currency of Internet storage and the Cloud (this could change very soon with the REST protocol, but that’s another story). Where else can you find a protocol where sharing is key. iSCSI, even though it has been growing at a faster pace in production storage, cannot be shared easily because it is block-based.

Now back to NFS. NFS version 3 has been around for more than 15 years and has taken its share of bad raps. I agree that this protocol is still very much in the landscape of most NFS installations. But NFS version 4 is changing all that taking on the better parts of the CIFS protocol, notably the equivalent of opportunistic locking or oplocks. In addition to that it has greatly enhanced its security, incorporating Kerberos-type of authentication. As for performance, NFS v4 added in a compounded in a COMPOUND operations for aggregating operations into a single request.

Today, most virtualization solutions from VMware and RedHat works with NFS natively. Note that the Windows CIFS protocol is not supported, only NFS.

This blog entry is not stating that NFS is better than iSCSI or FC but to give NFS credit where credit is due. NFS is not inferior to these block-based protocols. In fact, there are situations where NFS is better, like for instance, expanding the NFS-based datastore on the fly in a VMware implementation. I will use several performance related examples since performance is often used as a yardstick when these protocols are compared.

In an experiment conducted by VMware based on a version 4.0, with all things being equal, below is a series of graphs that compares these 3 protocols (NFS, iSCSI and FC). Note the comparison between NFS and iSCSI rather than FC because NFS and iSCSI run on Gigabit Ethernet, whereas FC is on a different networking platform (hey, if you got the money, go ahead and buy FC!)

Based a one virtual machine (VM), the Read throughput statistics (higher is better) are:


The red circle shows that NFS is up there with iSCSI in terms of read throughput from 4K blocks to 512K blocks. As for write throughput for 1 VM, the graph is shown below:

Even though NFS suffers in write throughput in the smaller blocks less than 16KB, NFS performance write throughput improves over iSCSI when between 16K and 32K range and is equal when it is in 64K, 128K and 512K block tests.

The 2 graphs above are of a single VM. But in most real production environment, a single ESX host will run multiple VMs and here is the throughput graph for multiple VMs.

Again, you can see that in a multiple VMs environment, NFS and iSCSI are equal in throughput, dispelling the notion that NFS is not as good in performance as iSCSI.

Oh, you might say that this is just VMs without any OSes or any applications running in these VMs. Next, I want to share with you another performance testing conducted by VMware for an Microsoft Exchange environment.

The next statistics are produced from an Exchange Load Generator (popularly known as LoadGen) to simulate the load of 16,000 Exchange users running in 8 VMs. With all things being equal again, you will be surprised after you see these graphs.

The graph above shows the average send mail latency of the 3 protocols (lower is better). On the average, NFS has lower latency than iSCSI, better than what most people might think. Another graph shows the 95th percentile of send mail latency below:


Again, you can see that the NFS’s latency is lower than iSCSI. Interesting isn’t it?

What about IOPS then? In another test with an 8-hour DoubleHeavy LoadGen simulator, the IOPS graphs for all 3 protocols are shown below:

In the graph above (higher is better), NFS performed reasonably well compared to the other 2 block-based protocols, and even outperforming iSCSI in this 8-hour load testing. Surprising huh?

As I have shown, NFS is not inferior compared to the block-based protocols such as iSCSI. In fact, VMware in version 4.1 has improved all 3 storage protocols significantly as mentioned in the VMware paper. The following are quoted in the paper for NFS and iSCSI.

  1. Using storage microbenchmarks, we observe that vSphere 4.1 NFS shows improvements in the range of 12–40% for Reads,and improvements in the range of 32–124% for Writes, over 10GbE.
  2. Using storage microbenchmarks, we observe that vSphere 4.1 Software iSCSI shows improvements in the range of 6–23% for Reads, and improvements in the range of 8–19% for Writes, over 10GbE

The performance improvement for NFS is significant when the network infrastructure was 10GbE. The percentage jump between 32-124%! That’s a whopping figure compared to iSCSI which ranged from 8-19%. Since both protocols are neck-to-neck in version 4.0, NFS seems to be taking a bigger lead in version 4.1. With the release of VMware version 5.0 a few weeks ago, we shall know the performance of both NFS and iSCSI soon.

To be fair, NFS does take a higher CPU performance hit compared to iSCSI as the graph below shows:

Also note that the load testing are based on NFS version 3. If version 4 was used, I am sure the performance statistics above will take a whole new plateau.

Therefore, NFS isn’t inferior at all compared to iSCSI, even in a 10GbE environment. We just got to know the facts instead of brushing off NFS.