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From Bryan Talbot <bryan.tal...@playnext.com>
Subject Re: Best partition type for Cassandra with JBOD
Date Mon, 19 May 2014 18:53:51 GMT
For XFS, using noatime and nodirtime isn't really useful either.

http://xfs.org/index.php/XFS_FAQ#Q:_Is_using_noatime_or.2Fand_nodiratime_at_mount_time_giving_any_performance_benefits_in_xfs_.28or_not_using_them_performance_decrease.29.3F




On Sat, May 17, 2014 at 7:52 AM, James Campbell <
james@breachintelligence.com> wrote:

>  Thanks for the thoughts!
> On May 16, 2014 4:23 PM, Ariel Weisberg <ariel@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 <
> james@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
>
>
>
>
> --
>
>
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-- 
Bryan Talbot
Architect / Platform team lead, Aeria Games and Entertainment
Silicon Valley | Berlin | Tokyo | Sao Paulo

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