Tom's statement below (to a NAC SAN when we build one) brings up a familiar argument between myself and my boss. My boss contends that NetApp is NOT capable of migrating to a "real SAN."
He bases this statement on his definition of SAN as "direct-attached storage (as in a direct SCSI connection) via a network of FiberChannel switches - but with the capability of also supporting NFS, CIFS, and HTTP mounts."
For instance, in a capability matrix of several vendors, which we recently compiled, he responds "yes" to the question of future SAN migration to an EMC, and to an EMC lookalike, Network Computers. To the same question, he responds "no" to the question of future SAN migration to a NetApp 740 cluster.
My position is -- when I see a SAN, I'll tell you what it is, but right now it's just an acronym for "Still Ain't None." I also contend that ALL of the storage vendors will implement SAN technology, if and when the technology gets fully defined and if and when the market demands it. In the meantime, I believe that NetApp is closer to being able to implement a SAN, than EMC and all of it's clones.
I also contend that SAN does NOT NECESSARILY imply FiberChannel. In fact, I see near-time SAN technology taking the route of 1000BaseT, because studies indicate that more (normal, read "small") data I/O's can be moved, much more cheaply, over Gigabit than over 100-base FiberChannel.
I expect in the future (when and if FiberChannel prices come down, and 1000-base, or 10,000-base FiberChannel is standard), it may become the defacto standard, but, for now, SCSI is the limiting factor on moving data, not the media speed.
Are there any experts out there who can shed some light on the subject?
Will Harper, MCSE
-----Original Message----- From: tkaczma@gryf.net [SMTP:tkaczma@gryf.net] Sent: Friday, March 26, 1999 1:30 AM To: NetApp Toasters (E-mail) Subject: Re: NDMP backup speeds
On Thu, 25 Mar 1999, Jason D. Kelleher wrote:
That sounds slow. We're readying an F740 for production and our tests show ~3MB/s (~11GB/hr) over a 110mb full-duplex connection to a Sun "backup server" with a DLT4000 jukebox.
Wow, I'm glad we back up to a locally attached tape library. I'd be even more glad to attach a bigger library to a NAC SAN when we build one.
Tom
<NAS != SAN stuff deleted>
Are there any experts out there who can shed some light on the subject?
Bah, it doesn't take an expert in my humble..
Filers are Network attached storage per their original definition. A SAN is a network that is dedicated to storage (summary of definition from the 2 articles that I've read from SunExpert and InfoWorld). Therefore if you happen to plug your NAS into a SAN, then it is part of the SAN by definition.
Just to give your boss an idea of how much this is all chopping words...
Tom's statement below (to a [NetApp] SAN when we build one) brings up a familiar argument between myself and my boss. My boss contends that NetApp is NOT capable of migrating to a "real SAN."
I've been delinquent in my duty of writing a NAS and SAN paper. I'm about half way done. Whem I'm done, I'll post it here, probably in early form, so that you guys can critique it for me.
Very briefly, I believe that NAS and SAN are different but related technologies, and that the definitions are as follows:
NAS (Network Attached Storage) Storage accessed over TCP/IP, using industry standard file sharing protocols like NFS, HTTP and Windows Networking.
SAN (Storage Area Network) Storage accessed over a Fibre Channel switching fabric, using encapsulated SCSI.
I also think that both NAS and SAN are useful, and that -- in the long run -- both will be critical components in any large data infrastructure. I think there's a strong analogy to the TCP/IP networking world. Routers and switches are very similar in some ways, yet subtly different in others. In the mid-eighties, arguments raged about which was "better". (Back then switches were called bridges.) Today we understand that any large network infrastructure needs to include both.
Some people would quibble with my definitions. Some would argue that if you run NFS over TCP/IP over fibre channel, then that is a SAN. I figure that we didn't invent new names for NFS over 100bT, FDDI, ATM, or Gigabit -- what's so special about fibre channel? Others argue that a SAN is any network dedicated entirely to storage traffic. Does this mean a SAN turns to a NAS if you fire up a telnet on it? A year ago these definitions were less settled, but today I think these are the definitions that are emerging.
With these definitions, the key difference is between file system protocols and raw disk protocols. With NAS, the filesystem runs on the storage system itself. (For NetApp, that's WAFL.) With SAN, the filesystem runs on the hosts attached to the storage system.
People familiar with EMC will recognize this model. With an EMC Symetrix, you get a big box of RAID protected disks, and you can attach multiple hosts to that one box. Thus, I view SAN as "open EMC". On the one hand, SAN could be viewed as a threat to EMC. But on the other hand, EMC has a solid history of products -- software and hardware -- based on this storage model, which means that they ought to have a real head-start on SAN. I think the SAN vendors have a great opportunity if they really can create "open EMC". After all, EMC is doing $4 Billion a year in business with this model!
In any case, I think NAS has some serious advantages over SAN. One big issue with running the file system on the separate hosts is that it makes true data sharing very difficult. The on-disk byte formats are very different between UNIX and NT, and even between different flavors of UNIX. Given the differences between UNIT and NT filesystem semantics, it's no surprise that the on-disk format is different. With NAS, the filesystem is by the data, so it can convert the on-disk format into an industry standard protocol appropriate to the host that wants the data: NFS for UNIX, NT Shares for NT, and HTTP for web browsers.
It is technically possible to build a "global file system" that has a common on-disk format for multiple operating systems, thus allowing NAS-like sharing for SAN. However, I'm skeptical of that model. First of all, there are no such products today. And even when they become available, sharing won't be based on industry standards. A system will only be able to participate in sharing if it runs a special SAN file system from a particular vendor. My believe is that the lesson of 20 years of networking is that we build heterogeneous environments by creating open standards and allowing everyone to support them -- not by saying that anyone who wants to participate in sharing must buy code from one particular company.
Having said all this, though, NetApp does have plans to leverage SAN technology. We have announced an OEM agreement with Brocade. Here are the benefits we expect to achieve:
- Attach to lots of disks.
A fibre channel loop is limited to 127 drives, but with a 16 port fibre channel switch, the limit goes to almost 2000 drives. With additional switches, you can support an arbitrary number of drives.
- Share tape drives between multiple servers.
I believe that backup applications are the killer application for SAN. When people buy expensive tape jukeboxes, they want to be able to attach them to multiple servers. With today's SCSI tapes that's a painful job. But with fibre channel and fibre channel switches, it's easy to connect a single tape to any number of hosts.
- Disaster Tolerant Solutions
Fibre channel switches can do WAN tunneling to provide connections to remote disks without any changes to the server code. This makes it much easier to build remote mirrors for data replication and disaster protection.
In conclusion, I believe that NAS and SAN are both important technologies, and the any large data infrastructure in the future will include both. I believe that NAS focuses on issues associated with users, applications, and data sharing. I believe that SAN focuses on issues associated with disk and tape devices, connection to large numbers of them, and moving data back and forth between them. In the long run, any large environment will have both sets of issues, and will need both types of solutions. In the short run, NAS makes good sense as a starting point, because it is here today and the standards it relies on have been solid for over a decade.
I'll go ahead an post the whole paper when I finish, but I still thought it might be useful to share my thoughts in this brief, half-baked form.
Dave
So, Dave, if I may get philisophical...
There are two ways to make technology progress, neither is better...
1. Decouple something into layers to add freedom: An application that uses NFS over RPC over TCP over IP over Ethernet over copper.
2. Merge layers to add speed: Network Attached Storage marries the filesystem layer and the disk layer, and marries all that to the network.
NetApps do #2. SANs do #1.
--tal
On Fri, 26 Mar 1999, Will Harper wrote:
Are there any experts out there who can shed some light on the subject?
It's not exactly an expert opinion, but Sun's monthly rant^H^H^H^H "Reality Check" column is about emerging SAN standards. I'll let the vendors fight it out, and in the meantime,I'll keep using what I know works *today*...
http://www.sun.com/realitycheck/headsup990302.html
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Brian Tao -
Dave Hitz -
Paul English -
Tom Limoncelli -
Will Harper