ZFS v VxFS - IOzone
By dom on Jan 04, 2007
IOzone is a I/O benchmarking utility that I have blogged about before. I also covered off the results of running Filebench on the two filesystems. Here, for the sake of completeness, are the results of some IOzone runs I did at the same time. The command line for IOzone used the following arguments and options:
iozone -R -a -z -b file.wks -g 4G -f testile
This test measures the performance of writing a new file. It is normal for the initial write performance to be lower than the performance of rewriting a file (see next test, below) due to metadata overhead.
Iozone Write Performance
This test measures the performance of writing a file that already exists. When a file is written that already exists the work required is less as the metadata already exists. It is normal for the rewrite performance to be higher than the performance of writing a new file.
Iozone Re-Write Performance
This test measures the performance of reading an existing file.
Iozone Read Performance
This test measures the performance of reading a file that was recently read. It is possible for the performance to be higher as the file system can maintain a cache of the data for files that were recently read. This cache can be used to satisfy reads and improves the throughput.
Iozone Re-read Performance
This test measures the performance of reading a file with accesses being made to random locations within the file. The performance of a system under this type of activity can be impacted by several factors such as the size of operating system’s cache, number of disks, seek latencies, and others.
Iozone Random Read Performance
This test measures the performance of writing a file with accesses being made to random locations within the file. Again the performance of a system under this type of activity can be impacted by the factors listed above for Random Read. Efficient random write is important to the operation of transaction processing systems.
Iozone Random Write Performance
This test measures the performance of reading a file backwards. This may seem like a strange way to read a file but in fact there are applications that do this. MSC Nastran is an example of an HPC application that reads its files backwards. Video editing is another example. Although many file systems have special features that enable them to read a file forward more rapidly, there are very few that detect and enhance the performance of reading a file backwards.
Iozone Backward Read Performance
This test measures the performance of writing and re-writing a particular spot within a file.
Iozone Record Rewrite Performance
This test measures the performance of reading a file with a strided access behavior. An example would be: “Read at offset zero for a length of 4 KB, then seek 200 KB, and then read for a length of 4 KB, then seek 200 KB and so on.” Here the pattern is to read 4 KB and then seek 200 KB and repeat the pattern. This again is a typical application behavior for applications that have data structures contained within a file and is accessing a particular region of the data structure. Most file systems do not detect this behavior or implement any techniques to enhance the performance under this type of access behavior.
Iozone Strided Read Performance
This test measures the performance of writing a file using the library function fwrite(). This is a library routine that performs buffered write operations. The buffer is within the user’s address space. If an application were to write in very small size transfers then the buffered & blocked I/O functionality of fwrite() can enhance the performance of the application by reducing the number of actual operating system calls and increasing the size of the transfers when operating system calls are made. This test is writing a new file so again the overhead of the metadata is included in the measurement.
Iozone fwrite() Performance
This test performs repetitive re-writes to portions of an existing file using the fwrite() interface.
Iozone Re-fwrite() Performance
This test measures the performance of reading a file using the library function fread() - a library routine that performs buffered & blocked read operations. The buffer is within the user’s address space, as for fwrite() operations. If an application were to read in very small size transfers then the buffered & blocked I/O functionality of fread() can enhance the performance of the application by reducing the number of actual operating system calls and increasing the size of the transfers when operating system calls are made.
Iozone fread Performance
This test is the same as fread() above except that in this test the file that is being read was read in the recent past. This can result in higher performance as the file system is likely to have the file data in cache.
Iozone Re-fread() Performance
In the last couple of blogs, I've given the results of testing a number of typical file system workloads in an open and reproduceable manner using the publicly available Filebench and IOzone tools and shown that Solaris 10 ZFS can significantly outperform a combination of Veritas Volume Manager and Filesystem in many cases. However, the following points (the "usual caveats") should also be taken into consideration:
- These tests were performed on a Sun Fire server with powerful processors, a large memory configuration, and a very wide interface to an array of high-speed disks to ensure that the fewest possible factors would inhibit file system performance. It is possible that the differences between file systems would be less pronounced on a less powerful system simply because all file systems would run into hardware bottlenecks in moving data to the disks.
- A file system performs only as well as the hardware and operating system infrastructure surrounding it, such as the virtual memory subsystem, kernel threading implementation, and device drivers. As such, Sun’s overall enhancements in the Solaris OS, combined with high-powered Sun Fire servers, will provide customers with high levels of performance for applications. But proof-of-concept (POC) implementations are invaluable in supporting purchasing decisions for specific configurations and applications.
- Benchmarks provide general guidance to performance. The conclusion that can be drawn from these tests is that in application areas such as databases, e-mail, web server and software development, Solaris 10 ZFS performs best in an “apples-to-apples” comparisons with the Veritas product suite. Again, POCs and real-world customer testing help evaluate performance for specific applications and services.