Gentlemen,
please have a look at this strange behaviour i came accross today:
The device i am working with is a 6way stripe over mirrors on a HSG80 in
transparent failover mode. Disks are 18GB scsi3 10krpm.
Chunk is 256kb. OS is Unix 5.1 on a DS40.
1. I create 5 files. While the first file is build no other IO is going to
the HSG80. The next 4 files are build in parallel using the '&' operator.
dd if=/dev/zero of=file1 bs=1024k count=1024
dd if=/dev/zero of=file2 bs=1024k count=1024 &
dd if=/dev/zero of=file3 bs=1024k count=1024 &
dd if=/dev/zero of=file4 bs=1024k count=1024 &
dd if=/dev/zero of=file5 bs=1024k count=1024 &
2. I monitor the IO throughput of a sequentiel read to the files with
iostat. The odd thing i found is this: The file that was build while no
other IO went to the device reads at about 51mb/sec. (dd if=file1
of=/dev/null bs=1024k). All files that where build in parallel only read
at about 20mb/sec, sometimes even much slower! I dont quite understand
why the fact whether files are written in parallel affects the read
performace in this configuration.
Thanks in advance,
--Armin
Received on Fri Nov 17 2000 - 20:57:10 NZDT