Escenario 1

As stated in bullet 5 of the objectives in Section 3.3, the analysis is compared and contrasted to previous similar work. The papers that are compared to the results from this thesis are “Workload Dependent Performance Evaluation of the Btrfs and ZFS Filesystems” by Heger (2009) and “BTRFS: The Linux B-Tree Filesystem” by Rodeh et. al. (2013). See Section 2.5 for a summary of the experimental setup used in the papers.

The experiments in this thesis have been designed to cover a lot of different scenarios so the result could be compare to related work. There are also many similarities between the experiments conducted in this thesis and the experiments in the two cited papers. This makes it possible to compare the result from this thesis to the cited papers even though they use different ways to measure the performance. However, since the hardware is different between the thesis and the referenced-to papers, the actual throughput is not relevant by itself, only how it relates to the other file systems that was tested on the same setup.

The results from the experiment with the single disk setup conducted by Heger (2009) differs drastically from the results found in this thesis. In Heger's experiment, ZFS outperformed Btrfs in all scenarios except for the sequential write operation where Btrfs had slightly higher throughput.

ZFS on Linux Btrfs

Maximum volume size _{256 ZiB (2}78 _{bytes) 16 EiB (2}64 _bytes)

Security Standard ACL Standard ACL

Stability Stable Medium (on-disk format is

stable but some features are still considered experimental)

Reliability End-to-end checksumming

of every data block and self healing of corrupt data

Checksums on data and metadata

Copy on Write Yes Yes

Snapshots Yes Yes

Volume resizing Expand but not shrink Yes

Transparent encryption No No

TRIM support (SSD optimization) Yes Yes

Data deduplication In-line deduplication (happens in real time)

Out-of-band deduplication (happens after writes, not during)

Compression Yes Yes

Table 1: Comparison of features between ZFS and Btrfs (Mills, 2014b; Bonwick et al. 2008; Sun Microsystems, Inc. 2006; OpenZFS, 2013; Btrfs Wiki, 2011; Btrfs Wiki, 2012).

sequential read. For the random read and random write Btrfs was performing better than ext4 but ZFS outperformed them both. Compared to the results in this thesis, ZFS and ext4 performed equally in the sequential read and write tests while Btrfs had the highest throughput. For the random read in this thesis, ext4 was performing slightly better than Btrfs but ZFS was performing significantly worse than both the other file systems. The random write was more even between the file systems but Btrfs had the highest throughput followed by ZFS and ext4 had the lowest throughput. The results of Heger's experiment of sequential read and write with the RAID 10 setup showed that Btrfs had significantly lower average throughput than both ZFS and ext4, which had similar throughput. In the random read and write tests Btrfs performed slightly better than ext4. ZFS however far outperformed them both in this experiment.

Heger's conclusions from the experiments was that for the single disk test, Btrfs was able to provide a good throughput relative to ext4 whereas ZFS performed similarly or better than ext4. For the RAID 10 experiments, Btrfs was not able to provide throughput results comparable to ext4 or ZFS. The performance of ZFS, although better than Btrfs, still trailed ext4 in all workload scenarios except for the random read and random write tests. Comparing these conclusions to the results from this thesis, the biggest difference is the performance of Btrfs that seems to have improved substantially. The performance of ZFS however seems to be at best on the same performance level compared to the other file systems but in some aspects much worse. Possible reasons for this could be that it is the result of the other file systems performance having improved, the specific experimental setup effecting the results, or the Linux implementation of ZFS that is not as refined as for other platforms.

The results from the macrobenchmark with the single disk setup conducted by Rodeh et al. (2013) in many ways are similar to the equivalent experiment in this thesis. For the Fileserver profile, Btrfs showed the highest performance, fairly closely followed by ext4, and then XFS with the lowest performance. This is the same trend as can bee seen from the results of this thesis. The OLTP result shows that the three file systems are fairly equal in performance with a slight advantage to Btrfs. The OLTP results for the single disk setup in this thesis however shows that Btrfs has lower average throughput than the other file systems. The result in the compared paper is however very similar to the results of the multiple disk setups in this thesis. Finally in the Webserver profile experiment, Btrfs and XFS show similar throughput whereas ext4 shows a significantly higher performance. Compared to the results in this thesis the performance was very similar between all the file systems. The microbenchmarks with RAID 10 setup conducted by Rodeh et al. (2013) consisted of sequential read and write of large files. In the write test, Btrfs and XFS showed similar performance. The read test showed a bit of a difference between the file systems as Btrfs had slightly higher throughput than XFS. Compared to this thesis the result of the write test is the same as the performance is very similar for Btrfs and XFS.

7 Conclusion

In this thesis, a performance comparison between Btrfs and ZFS has been made by conducting a set of experiments. The file systems was also compared against the most common Linux file systems today, XFS and ext4. The experiments tested the average throughput for both single I/O operations and a combination of different workloads to emulate real usage. Further, different disk configurations was used. First a single disk setup was tested, then a RAID 10 setup and finally a RAID 5 setup. The result was then analyzed and compared to previous studies. In addition to this, a qualitative analysis of other important features was done.

The conclusion of the main findings is that Btrfs showed a high average throughput for most of the tests, compared to the other file systems. By comparing the results to the results from previous similar work it shows that the performance has improved greatly in recent years, especially the multiple disk performance. Btrfs has had big problems with the stability of RAID 5 and RAID 6 and only in the latest Linux kernel, at the time of writing, was it considered stable. Therefore a RAID 5 setup was also included in the experiments and the results surprisingly showed that Btrfs had significantly higher average throughput than the other file systems. ZFS however did not perform as well but the exact reason for this could not be established from the data gathered in the experiments, but is instead listed as in the future work section (see Section 7.3).