Parallel File System Simulator In order to test the Parallel File System (PFS) scheduling algorithms in a light-weighted approach, we have developed the PFS simulator. We use discrete event simulator and accurate disk modeling software to construct an agile parallel file system simulator. This simulator is capable of simulating enough details while having an acceptable simulation time. 1 HEC FSIO 2009 tests.

Existing PFS simulators The IMPIOUS simulator, by E Molina-Estolano, al. et[1]. It does not model the metadata server. The scheduler modules are lacking, so scheduling algorithms are hard to model. The simulator developed in PVFS improvement paper by Carns P. H., al. et[2]. It over simulates the network, which extends the simulation time. It uses real PVFS in simulation, which introduces too much details, while not flexible. 2 HEC FSIO 2009

Simulator Details We use the discrete event simulation library OMNeT to simulate the network. It is capable of simulating the network topology with bandwidth and delay. We use Disksim to simulate the data server disks. Disksim accurately estimates the time for data transactions on the physical disks. Disksim allows users to extract disk characteristics from real disks. 3 HEC FSIO 2009

Simulator Architecture 4 HEC FSIO 2009 Client trace Metadata Server Stripping Strategy Client trace Client trace Simulated Network OMNeT++ Disksims instances Data Servers Scheduling Algorithm Socket Connections Metadata Server Local FS Disk queue Local FS Disk queue Local FS Disk queue output New request arrives. Query file layout. Send the request to data server. Dispatch the job. Send the results back.

Implementation of Scheduling Algorithms Similarly, we have also implemented FIFO, Distributed SFQ[3], MinSFQ[4] algorithms, etc. 5 HEC FSIO 2009 /* SFQ algorithm, at each data server */ systime = 0 waitQ.initiate() while(!simulation_end) { if reqArrive(), then: R = getReq() R.start_tag = min { R.getPrevReq().finish_tag, systime } R.finish_tag = R.start_tag + R.cost / R.getFlow().weight pushReq(R, waitQ) if diskHasSlot(), then: R = popReqwithMinStartTag(waitQ) systime = R.start_tag dispatch(R) } The request from client arrives at the data server. Disksim tells OMNet++ that it still has free slot. OMNet++ dispatches the request to Disksim.

Simulation 1: Weighted Scheduling 2 groups of clients, 16 each. 4 Data servers and 1 Metadata server. Parallel Virtual File System(v2) is modeled. All files striped to all servers. Stripe size: 256KB. The trace files are generated by IOR. Each client has 100MB checkpoint-write operation. SFQ with different weight assignments have been simulated. The simulated weight ratios are 1:1, 2:1 and 10:1. 6 HEC FSIO 2009

Throughput Results 7 HEC FSIO 2009

Simulation 2: Scheduling Fairness Same as Simulation 1, except that the two groups do not have the same resources: Group 1s files are stripped to all servers [1, 2, 3, 4]. Group 2s files are stripped to 3 servers [1, 2, 3]. We add Distributed SFQ algorithm[3], in which all servers share the scheduling information. We are able to show that if the workloads are not evenly distributed, the Distributed SFQ algorithm achieves better fairness than FIFO and SFQ. 8 HEC FSIO 2009

Throughput Results 9 HEC FSIO 2009

References [1] E Molina-Estolano, C Maltzahn, J Bent and S A Brandt, Building a parallel file system simulator, Journal of Physics: Conference Series 180 (2009) [2] Carns P H, Ligon W B, al. et. Using Server-to-Server Communication in Parallel File Systems to Simplify Consistency and Improve Performance, Proceedings of the 4 th Annual Linux Showcase and Conference (Atlanta, GA) pp [3] Yin Wang and Arif Merchant, Proportional Share Scheduling for Distributed Storage Systems, File and Storage Technologies (FAST07), San Jose, CA, February [4] W. Jin, J. S. Chase and J. Kaur, Interposed Proportional Sharing For A Storage Service Utility, SIGMETRICS, E. G. C. Jr., Z. Liu, and A. Merchant, Eds. ACM, 2004, pp HEC FSIO 2009