Eric is right on.
Let me share my experience. I have found that dense nodes over 4 TB are a pain
to manage (for rebuilds, repair, compaction, etc.) with size-tiered compaction
and basically a single table schema. However, 1 TB nodes that yield only about
500 GB of usable space can create rings with just too many nodes (and too
expensive for the usable storage). 2 TB seems to be a good sweet spot to avoid
either extreme. However, Eric is correct, there are lots of factors to weigh in
the decision.
Sean Durity – Lead Cassandra Admin
From: Eric Stevens [mailto:migh...@gmail.com]
Sent: Monday, May 30, 2016 10:56 AM
To: user@cassandra.apache.org
Subject: Re: Per node limit for Disk Space
Those are rough guidelines, actual effective node size is going to depend on
your read/write workload and the compaction strategy you choose. The biggest
reason data density per node usually needs to be limited is due to data
grooming overhead introduced by compaction. Data at rest essentially becomes
I/O debt. If you're using Leveled compaction, the interest rate on that debt
is higher.
If you're writing aggressively you'll find that you run out of I/O capacity for
smaller data at rest. If you use compaction strategies that allow for data to
eventually stop compacting (Date Tiered, Time Windowed), you may be able to
have higher data density per node assuming that some of your data is going into
the no-longer-compacting stages.
Beyond that it'll be hard to say what the right size for you is. Target the
recommended numbers and if you find that you're not running out of I/O as you
approach them you can probably go bigger. Just remember to leave ~50% disk
capacity free to leave room for compaction to happen.
On Fri, May 27, 2016 at 1:52 PM Anshu Vajpayee
<anshu.vajpa...@gmail.com<mailto:anshu.vajpa...@gmail.com>> wrote:
Hi All,
I have question regarding max disk space limit on a node.
As per Data stax, We can have 1TB max disk space for rotational disks and up to
5 TB for SSDs on a node.
Could you please suggest per your experience what would be limit for space on a
single node with out causing so much stress on a node?
Thanks,
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