Thanks for the thoughts! On May 16, 2014 4:23 PM, Ariel Weisberg <ar...@weisberg.ws> wrote: Hi,
Recommending nobarrier (mount option barrier=0) when you don't know if a non-volatile cache in play is probably not the way to go. A non-volatile cache will typically ignore write barriers if a given block device is configured to cache writes anyways. I am also skeptical you will see a boost in performance. Applications that want to defer and batch writes won't emit write barriers frequently and when they do it's because the data has to be there. Filesystems depend on write barriers although it is surprisingly hard to get a reordering that is really bad because of the way journals are managed. Cassandra uses log structured storage and supports asynchronous periodic group commit so it doesn't need to emit write barriers frequently. Setting read ahead to zero on an SSD is necessary to get the maximum number of random reads, but will also disable prefetching for sequential reads. You need a lot less prefetching with an SSD due to the much faster response time, but it's still many microseconds. Someone with more Cassandra specific knowledge can probably give better advice as to when a non-zero read ahead make sense with Cassandra. This is something may be workload specific as well. Regards, Ariel On Fri, May 16, 2014, at 01:55 PM, Kevin Burton wrote: That and nobarrier... and probably noop for the scheduler if using SSD and setting readahead to zero... On Fri, May 16, 2014 at 10:29 AM, James Campbell <ja...@breachintelligence.com<mailto:ja...@breachintelligence.com>> wrote: Hi all- What partition type is best/most commonly used for a multi-disk JBOD setup running Cassandra on CentOS 64bit? The datastax production server guidelines recommend XFS for data partitions, saying, "Because Cassandra can use almost half your disk space for a single file, use XFS when using large disks, particularly if using a 32-bit kernel. XFS file size limits are 16TB max on a 32-bit kernel, and essentially unlimited on 64-bit." However, the same document also notes that "Maximum recommended capacity for Cassandra 1.2 and later is 3 to 5TB per node," which makes me think >16TB file sizes would be irrelevant (especially when not using RAID to create a single large volume). What has been the experience of this group? I also noted that the guidelines don't mention setting noatime and nodiratime flags in the fstab for data volumes, but I wonder if that's a common practice. James -- Founder/CEO Spinn3r.com<http://Spinn3r.com> Location: San Francisco, CA Skype: burtonator blog: http://burtonator.wordpress.com ... or check out my Google+ profile<https://plus.google.com/102718274791889610666/posts> [http://spinn3r.com/images/spinn3r.jpg]<http://spinn3r.com> War is peace. Freedom is slavery. Ignorance is strength. Corporations are people.
