On Thu, 15 Oct 2009 11:32:35 +0200 Usman Waheed <usm...@opera.com> wrote:
> Hi Todd, > > Some changes have been applied to the cluster based on the > documentation (URL) you noted below, I would also like to know what settings people are tuning on the operating system level. The blog post mentioned here does not mention much about that, except for the fileno changes. We got about 3x the read performance when running DFSIOTest by mounting our ext3 filesystems with the noatime parameter. I saw that mentioned in the slides from some Cloudera presentation. (For those who don't know, the noatime parameter turns off the recording of access time on files. That's a horrible performance killer since it means every read of a file also means that the kernel must do a write. These writes are probably queued up, but still, if you don't need the atime (very few applications do), turn it off!) Have people been experimenting with different filesystems, or are most of us running on top of ext3? How about mounting ext3 with "data=writeback"? That's rumoured to give the best throughput and could help with write performance. From mount(8): writeback Data ordering is not preserved - data may be written into the main file system after its metadata has been committed to the journal. This is rumoured to be the highest throughput option. It guarantees internal file system integrity, however it can allow old data to appear in files after a crash and journal recovery. How would the HDFS consistency checks cope with old data appearing in the unerlying files after a system crash? Cheers, \EF -- Erik Forsberg <forsb...@opera.com> Developer, Opera Software - http://www.opera.com/