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Date: Fri, 10 Apr 2015 16:30:34 -0700
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Subject: Re: Moving SSTables from one disk to another
From: Jonathan Haddad <jon@jonhaddad.com>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
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I had submitted this issue which could have had (in theory) some
serious performance benefit when using JBOD:
https://issues.apache.org/jira/browse/CASSANDRA-8868

However, it was pointed out to me that
https://issues.apache.org/jira/browse/CASSANDRA-6696 will be a better
solution in a lot of cases.

On Fri, Apr 10, 2015 at 4:13 PM, Robert Coli <rcoli@eventbrite.com> wrote:
> On Fri, Apr 10, 2015 at 4:00 PM, Roman Tkachenko <roman@mailgunhq.com>
> wrote:
>>
>> * Can I just move some SSTables data files from "sstables2" to "sstables1"
>> which has much more free disk space? Will Cassandra start fine after that
>> and not lose any data?
>
>
> Cassandra generally discovers files in its data directories and treats them
> as legitimate files. I do not have specific knowledge of JBOD behavior here,
> but I would presume it would be the same.
>
>>
>> * Provided multiple data dirs, should Cassandra distribute data equally
>> between them? In what I'm observing this is almost always not true. On that
>> particular node I mentioned above the difference is huge: 4% occupied disk
>> space for "sstables1" and 87% for "sstables2"; on other nodes the situation
>> is a little better but still not 50/50.
>
>
> No, and especially not when using Size Tiered Compaction.
>
> I honestly wonder why people think JBOD is a useful feature for Cassandra.
> You don't really want to continue to operate a node that has lost half of
> its data, and managing multiple data directories seems relatively likely to
> be more trouble than it's worth. You have a distributed, replicated
> database... just replace nodes when they fail. Anyone care to set me
> straight about the amazing benefits they see which make the costs
> worthwhile?
>
> =Rob
>


-- 
Jon Haddad
http://www.rustyrazorblade.com
twitter: rustyrazorblade