1. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 1 Hard Disk Drive Traffic Model for TGad Date: 2009-11-17 Authors:

2. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 2 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

3. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 3 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

4. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 4 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

5. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 5 Measured Transaction Size Most of the transaction are 64 Kbytes and 128 Kbytes

6. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 6 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

7. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 7 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

8. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 8 Model Step 1: Compute sequence of inter-arrival times of transaction requests Step 2: Compute corresponding sequence of transaction data sizes

9. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 9 Transaction Data Size Model Discrete Random Variable distribution

10. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 10 Inter-arrival Times of Transaction Requests Model Discrete Random Variable distribution

11. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 11 Simulated Inter-Arrival Time of Requests Simulated “time” is derived by a cumulative sum of the inter- arrival time

12. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 12 Simulated Transaction Size Simulated average data rate over the entire period is equal to 30Mbps

13. doc.: IEEE 802.11-09/1222r1 Submission November 2009 Eldad Perahia, Intel CorporationSlide 13 Conclusion Incorporate described hard disk drive model into Evaluation Methodology document