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Sensitivity of Cluster File System Access to I/O Server Selection. A. Apon, P. Wolinski, and G. Amerson University of Arkansas. Overview. Benchmarking study Parallel Virtual File System (PVFS) Network File System (NFS) Testing parameters include Pentium-based cluster node hardware

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sensitivity of cluster file system access to i o server selection

Sensitivity of Cluster File System Access to I/O Server Selection

A. Apon, P. Wolinski,

and G. Amerson

University of Arkansas

overview
Overview
  • Benchmarking study
    • Parallel Virtual File System (PVFS)
    • Network File System (NFS)
  • Testing parameters include
    • Pentium-based cluster node hardware
    • Myrinet interconnect
    • Varying number and configuration of I/O servers and client request patterns
outline
Outline
  • File system architectures
  • Performance study design
  • Experimental results
  • Conclusions and future work
nfs architecture
NFS Architecture
  • Client/server system
  • Single server for files

NFS Server

Node 1

Each cluster node has

dual-processor Pentium

Linux, HD, lots of memory

Node 0

Node 2

Network Switch

DATA

FILE

Node N

pvfs architecture

Node 0

Node 2

Node 1

PVFS Architecture
  • Also a client/server system
  • Many servers for each file
  • Fixed sized stripes in round-robin fashion

DATA

FILE

Network Switch

Each cluster node still has

dual-processor Pentium

Linux, HD, lots of memory

pvfs architecture1
PVFS Architecture
  • One node is a manager node
    • Maintains metadata information for files
  • Configuration and usage options include:
    • Size of stripe
    • Number of I/O servers
    • Which nodes serve as I/O servers
    • Native PVFS API vs. UNIX/POSIX API
native pvfs api example
Native PVFS API example

#include <pvfs.h>

int main() {

int fd, bytes;

fd=pvfs_open(fn,O_RDONLY,0,NULL,NULL);

...

pvfs_lseek(fd, offset, SEEK_SET);

...

bytes_read = pvfs_read(fd, buf_ptr, bytes);

...

pvfs_close(fd);

}

performance study design
Performance Study Design
  • Goals
    • Investigate the effect on cluster I/O when using the NFS server or the PVFS I/O servers also as clients
    • Compare PVFS with NFS
performance study design1
Performance Study Design
  • Experimental cluster
    • Seven dual-processor Pentium III 1GHz, 1GB memory computers
    • Dual EIDE disk RAID 0 subsystem in all nodes, measured throughput about 50MBps
    • Myrinet switches, 250MBps theoretical bandwidth
performance study design2
Performance Study Design
  • Two extreme client workloads
    • Local whole file (LWF)
      • Takes advantage of caching on server side
      • One process per node, each process reads the entire file from beginning to end

Node 1

Node 2

Node N

performance study design3
Performance Study Design
  • Two extreme client workloads
    • Global whole file (GWF)
      • Minimal help from caching on the server side
      • One process per node, each process reads a different portion of the file, balanced workload

Node 1

Node 2

Node N

nfs parameters
NFS Parameters
  • Mount on Node 0 is a local mount
    • Optimization for NFS
  • NFS server can participate or not as a client in the workload
pvfs parameters
PVFS Parameters
  • A preliminary study was performed to determine the “best” stripe size and request size for the LWF and GWF workloads
    • Stripe size of 16KB
    • Request size of 16MB
    • File size of 1GB
  • All I/O servers for a given file participate in all requests for that file
system software
System Software
  • RedHat Linux version 7.1
  • Linux kernel version 2.4.17-rc2
  • NFS protocol version 3
  • PVFS version 1.5.3
  • PVFS kernel version 1.5.3
  • Myrinet network drivers gm-1.5-pre3b
  • MPICH version 1.2.1
experimental pseudocode
Experimental Pseudocode

For all nodes

Open the test file

Barrier synchronize with all clients

Get start time

Loop to read/write my portion

Barrier synchronize with all clients

Get end time

Report bytes processed and time

For Node 0

Receive bytes processed, report aggregate throughput

clearcache
Clearcache
  • Clear NFS client and server-side caches
    • Unmount NFS directory, shutdown NFS
    • Restart NFS, remount NFS directories
  • Clear server-side PVFS cache
    • Unmount PVFS directories on all nodes
    • Shutdown PVFS I/O daemons, manager
    • Unmount pvfs-data directory on slaves
    • Restart PVFS manager, I/O daemons
    • Remount PVFS directories, all nodes
experimental parameters
Experimental Parameters
  • Number of participating clients
  • Number of PVFS I/O servers
  • PVFS native API vs. UNIX/POSIX API
  • I/O servers (NFS as well as PVFS) may or may not also participate as clients
experimental results
Experimental Results
  • NFS
  • PVFS native API vs UNIX/POSIX API
  • GWF, varying server configurations
  • LWF, varying server configurations
conclusions
Conclusions
  • NFS can take advantage of a local mount
  • NFS performance is limited by contention at the single server
    • Limited to the disk throughput or the network throughput from the server, whichever has the most contention
conclusions1
Conclusions
  • PVFS performance generally improves (does not decrease) as the number of clients increases
    • More improvement seen with LWF workload than with the GWF workload
  • PVFS performance improves when the workload can take advantage of server-side caching
conclusions2
Conclusions
  • PVFS is better than NFS for all types of workloads where more than one I/O server can be used
  • PVFS UNIX/POSIX API performance is much less than the performance using the PVFS native API
    • May be improved by a new release of the Linux kernel
conclusions3
Conclusions
  • For a given number of servers, PVFS I/O throughput decreases when the servers also act as clients
  • For the workloads tested, PVFS system throughput increases to the maximum possible for the cluster when all nodes participate as both clients and servers
observation
Observation
  • The drivers and libraries have been in constant upgrade during these studies. However, our recent experiences indicate that they are now stable and interoperate well together.
future work
Future Work
  • Benchmarking with cluster workloads that include both computation and file access
  • Expand the benchmarking to a cluster with a higher number of PVFS clients and PVFS servers
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