[Beowulf] Any recommendations for a good JBOD?

Patrick Geoffray patrick at myri.com
Mon Feb 22 15:58:15 EST 2010


Joe,

On 2/19/2010 9:52 PM, Joe Landman wrote:
> This aside, both AoE and iSCSI provide block device services. Both
> systems can present a block device with a RAID backing store. Patrick
> and others will talk about the beauty of the standards, but this is
> unfortunately irrelevant in the market. The market isn't a meritocracy.

Indeed, this is unfortunate. To be clear, I did not comment on the 
implementations, only the protocols. And on that point, iSCSI is 
definitively one of the worst spec I have ever read. The fact that iSCSI 
has any traction is a good example that marketers are in command, not 
engineers.

I would not say that the quality of the protocol is irrelevant, it has a 
direct impact on the robustness and performance of the implementations. 
For example, any kind of offload requires the iSCSI header to be at the 
beginning of a packet, so you need framing. However, iSCSI is build on 
top of TCP, a streaming protocol. So, if you go through a router and 
change MTU, you are toast. The worse part is that the iSCSI standard 
acknowledges that but the solution they propose is ridiculous (PDU markers).

FCoE shares some of the simplicity of AoE (right on top of Ethernet), 
but then the marketers came and messed it up with all kind of extensions 
to justify selling you new (and expensive) gear.

> Actually, with the advent of USB3 and related devices, I'd expect AoE
> and lower end raid to be effectively completely subsumed by this. USB3
> has ample bandwidth to connect a low end RAID unit, more than GbE. The

You can't switch USB the same way you switch Ethernet.

Patrick
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