An Investigation into Transport Protocols and Data Transport ...

A.1. Data Storage 263
gether with high capacity and storage efficiency. Due to the inclusion
of the parity data total write speeds are slower than for RAID-0. Total
read speeds are also slower as the parity stripes must be skipped over
in order to reach the ordinary data stripes.
A.1.2
Test Methodology
A set of tests were performed to compare the read and write speeds of a selection
of RAID controllers. RAID configurations were chosen to compare and
contrast the optimal performance configuration of RAID-0, and an optimum
real life implementation with RAID-5.
Only the transfer of large data-sets is considered where it is assumed that
the data is stored in a roughly linear manner whereby hard disk seek times
may be neglected 2 .
All tests were performed on ‘server-class’ PC’s as shown in Table A.1
with the associated RAID controller cards as shown in Table A.2. The disks
used in all tests are shown in Table A.3 and were formatted with the ext2
file system that is representative of most Linux based systems which are
prevalent in research communities.
Two separate programs were created to perform the reading and writing
of data to and from user space. They implement the standard read() and
write() Unix calls. Given a predefined file or file size, the read() program
reads data from the RAID partition into a circular buffer in memory. The
write() program writes a defined size of random data from memory onto
disk.
The vm.max-readahead sysctl [Rub97] in Linux affects how early the
2 It is also assumed that the presence of file fragmentation is negligible.