[Pvfs2-users] collective IO performance

[Xinhua Gao]

Hello,

I am using IOR to write/read a shared file with up to 16 processes, each
writing data of 128M in units of 256K. Here is the data I got with
collective IO and independent IO.

# collective IO 
#procs write read
 2  74.53 12.43
 4  36.28 15.85
 6  20.66 18.61
 8  20.16 23.57
10  22.18 33.15
12  24.18 49.36

# independent IO to a single file
# proc   write   read (MB/sec)
 2   51.98   28.55
 4   65.15   55.73
 6   83.03   70.01
 8   98.96   82.06
10   124.65   102.35
12   126.86   112.36
14   139.63   119.50
16   147.01   154.90

It is a little surprising to see collective IO performance is so low
compared to independent IO. In addition, collective IO does not increase
with increasing number of clients. The set servers has 5 IO servers can
support at least 100MB/sec of IO rates directly from disks.

Anybody can provide some hints? Thanks,

Xinhua