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

2. 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

3. 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

4. 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

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

6. 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

7. 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

8. 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

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

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

11. 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

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

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