SATAnet Networking Characteristics

The information on this page is preliminary and the product is currently subject to improvement.

Contents
1 » Bandwidth2 » Latency
Bandwidth
  • Can determine the dataset sizes for batch-style parallelism — effectively a latency
  • Can determine the processing speed for stream-based parallelism
  • Low bandwidth is acceptable with highly-independent parallelism
  • High bandwidth is beneficial for highly-dependent parallelism

A node can be connected to one or more SATAnet routers and to one or more ports per router. Using multiple ports allows for multiplication of the bandwidth and also lower average latency.

The following table lists bandwidths for packet transfers of varying sizes on a SATA-I interface.

Graph
Packet size (bytes) Bandwidth (Mbytes/s)
512 8.5
1024 11.9
2048 21.9
4096 36.9
8192 56.6
16384 72.2
Latency
  • Can determine the granularity of the parallelism
  • Low-latency is important in synchronous or poorly-parallel applications
  • High-latency is tolerable in asynchronous and highly-parallel applications
  • Set-up latencies can be offset by merging packets
  • In core-rich nodes one core can be allocated to communications to minimise blocking

Packet-switched latencies

The following table lists timings for a packet to transfer through various parts of a Linux-based system.

Metric Symbol Time (µs)
Application to driver Ttad 2
Driver to SATA host Ttdh 60
Host to host via SATAnet switchTnet 0.2
SATA host to driver Trhd 60
Driver to application Trda 2

Transmission on one node is asynchronous to reception on another node, and so the latencies overlap. In practice this means that the overall latency is lower than the simple summation of each part of the transfer. Since the latencies are roughly symmetrical for both transmission and reception, the typical overall latency is Ttad + Ttdh + Tnet = 62µs.

Circuit-switched latencies

The following table lists the approximate timings for a 4-byte word to transfer through various parts of a Linux-based system.

Metric Symbol Time (µs)
Application to SATAhost Ttah0.3
Host to host via SATAnet switchTnet0.2
SATAhost to application Trha0.3

Total end-to-end latency is simply Ttah + Tnet + Trha = 0.8µs. The bandwidth achieved for back-to-back transfers of 4-byte words is around 8~12Mbytes/sec.

Technology in brief

A cluster communication interconnect which can be utilised without special drivers by any platform which supports Serial ATA connectivity regardless of architecture and operating system.

The unique approach also offers “centralised distributed” storage, allowing a physically remote disc to be accessed as a local disc — reduces heat, noise, and vibration, improves cooling, and removes points of failure within cluster nodes.

Technology reports


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Function


Arrangement

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Performance


Networking characteristics

Storage characteristics

Related technology


Cortica

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