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From Tyler Hobbs <ty...@riptano.com>
Subject Re: Cassandra and disk space
Date Thu, 09 Dec 2010 19:26:42 GMT
That depends on your scenario.  In the worst case of one big CF, there's not
much that can be easily done for the disk usage of compaction and cleanup
(which is essentially compaction).

If, instead, you have several column families and no single CF makes up the
majority of your data, you can push your disk usage a bit higher.

A fundamental idea behind Cassandra's architecture is that disk space is
cheap (which, indeed, it is).  If you are particularly sensitive to this,
Cassandra might not be the best solution to your problem.  Also keep in mind
that Cassandra performs well with average disks, so you don't need to spend
a lot there.  Additionally, most people find that the replication protects
their data enough to allow them to use RAID 0 instead of 1, 10, 5, or 6.

- Tyler

On Thu, Dec 9, 2010 at 12:20 PM, Rustam Aliyev <rustam@code.az> wrote:

>  Is there any plans to improve this in future?
>
> For big data clusters this could be very expensive. Based on your comment,
> I will need 200TB of storage for 100TB of data to keep Cassandra running.
>
> --
> Rustam.
>
> On 09/12/2010 17:56, Tyler Hobbs wrote:
>
> If you are on 0.6, repair is particularly dangerous with respect to disk
> space usage.  If your replica is sufficiently out of sync, you can triple
> your disk usage pretty easily.  This has been improved in 0.7, so repairs
> should use about half as much disk space, on average.
>
> In general, yes, keep your nodes under 50% disk usage at all times.  Any
> of: compaction, cleanup, snapshotting, repair, or bootstrapping (the latter
> two are improved in 0.7) can double your disk usage temporarily.
>
> You should plan to add more disk space or add nodes when you get close to
> this limit.  Once you go over 50%, it's more difficult to add nodes, at
> least in 0.6.
>
> - Tyler
>
> On Thu, Dec 9, 2010 at 11:19 AM, Mark <static.void.dev@gmail.com> wrote:
>
>> I recently ran into a problem during a repair operation where my nodes
>> completely ran out of space and my whole cluster was... well, clusterfucked.
>>
>> I want to make sure how to prevent this problem in the future.
>>
>> Should I make sure that at all times every node is under 50% of its disk
>> space? Are there any normal day-to-day operations that would cause the any
>> one node to double in size that I should be aware of? If on or more nodes to
>> surpass the 50% mark, what should I plan to do?
>>
>> Thanks for any advice
>>
>
>

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