Hard Disk Drive Traffic Model for TGad April 2007 doc.: IEEE 802.11-07/0570r0 November 2009 Hard Disk Drive Traffic Model for TGad Date: 2009-11-17 Authors: Eldad Perahia, Intel Corporation Eldad Perahia, Intel Corporation

November 2009 Background TGad Evaluation Methodology document includes a “hard disk file transfer” application Enterprise cubicle scenario File transfer wirelessly between laptop and hard drive Traffic model is TBD Eldad Perahia, Intel Corporation

Measured Data and Modeling November 2009 Measured Data and Modeling Hard Disk test in the PCMark Vantage benchmarking suite used to capture sample trace Specific subtest captured was “Importing pictures to Windows Photo Gallery” Reading a large collection of picture files from the hard drive Data captured is the transactions size and request time of the transactions Transactions are all reads from the hard drive Requests can be overlapping in time, i.e. a subsequent request arrives before the previous transaction is complete Model of the offered load of the transaction (packet size) and inter-arrival time of the requests is created with discrete random distributions Eldad Perahia, Intel Corporation

November 2009 Transaction model A transaction consists of a READ request from host to drive for a specific block of data Followed by the data transfer from drive to host For the purpose of the model: READ request is a short (256B) packet sent from host to drive Data transfer is instantaneous delivery of 4kB – 128kB to transmit queue in drive to host direction Assume fixed 1ms delay between receipt of READ request and data offered In practice, delay varies based on seek latencies of drive Not a significant component of the model READ (256B) Data (4kB-128kB) Inter-arrival time Inter-arrival time Eldad Perahia, Intel Corporation

Measured Transaction Size November 2009 Measured Transaction Size Most of the transaction are 64 Kbytes and 128 Kbytes Eldad Perahia, Intel Corporation

Measured Inter-Arrival Time of Requests November 2009 Measured Inter-Arrival Time of Requests Large grouping of inter-arrival times between 40usec and 1.1msec Inter-arrival times of requests of 40usec indicate overlapping requests Also high frequency of inter-arrival times of 50msec Probably due to operating system processing delay Eldad Perahia, Intel Corporation

Data Rate of Measured Data based on Transaction Completion Time November 2009 Data Rate of Measured Data based on Transaction Completion Time Maximum data rate equals 2.2 Gbps Average data rate (total transaction/total time) = 31 Mbps Eldad Perahia, Intel Corporation

November 2009 Model Step 1: Compute sequence of inter-arrival times of transaction requests Step 2: Compute corresponding sequence of transaction data sizes Eldad Perahia, Intel Corporation

Transaction Data Size Model November 2009 Transaction Data Size Model Discrete Random Variable distribution Eldad Perahia, Intel Corporation

Inter-arrival Times of Transaction Requests Model November 2009 Inter-arrival Times of Transaction Requests Model Discrete Random Variable distribution Eldad Perahia, Intel Corporation

Simulated Inter-Arrival Time of Requests November 2009 Simulated Inter-Arrival Time of Requests Simulated “time” is derived by a cumulative sum of the inter-arrival time Eldad Perahia, Intel Corporation

Simulated Transaction Size November 2009 Simulated Transaction Size Simulated average data rate over the entire period is equal to 30Mbps Eldad Perahia, Intel Corporation

November 2009 Conclusion Incorporate described hard disk drive model into Evaluation Methodology document Eldad Perahia, Intel Corporation