On Sat, Apr 5, 2014 at 12:59 PM, Edward Ned Harvey (lopser) < [email protected]> wrote:
> > I disagree bigtime. Even if you run iscsi over 10Ge, it still has to go > through all the mac/ip/application layers, not to mention, the 10Ge switch, > probably buffering, store and forward, etc. If you have a network such as > Infiniband or Fibre Channel, you're able to skip all those and use DMA > directly, which greatly decreases latency. Also, the speed of even the > slowest IB network is around 40 Gbit, while ether maxes out at 10Gbit. > > Whether using SSD or HDD, the sustainable throughput of each individual > device is around 1Gbit. So the max performance of a 10Ge network is on-par > with 10 disks. Which would be a pathetically small SAN. > > Ed, Any well designed iscsi or fcoe system will offload that overhead to a dedicated HBA. Certainly if you're talking high performance you won't be using a software iscsi initiator on the host. I also think you should spend some time getting caught up on the recent advances in switching, both in design and the low level performance. In addition to the design stuff I mentioned elsewhere in the thread, modern 10g switches have latency as low as 1 microsecond, or even lower in a few brands (I believe Mellanox was touted as 200 nanosecond latency), and do cut-through switching where the packet has started leaving the switch before it's even fully arrived. > Whether using SSD or HDD, the sustainable throughput of each individual device is around 1Gbit. So the max performance of a 10Ge network is on-par with 10 disks. Which would be a pathetically small SAN. Yet many SANs get away with a single or dual 8g fc interface to the array. If you're looking for real performance you need a massively scaled array with many connections to the data fabric, whether it's Ethernet or fibre channel. -David
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