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.
Is there any formula to calculate this? Let's say I have 500GB in single
CF. So I need at least 500GB of free space for compaction. If I
partition this CF and split it into 10 proportional CFs each 50GB, does
it mean that I will need only 50GB of free space?
Also, is there recommended maximum of data size per node?
Thanks.
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 <rus...@code.az
<mailto:rus...@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....@gmail.com
<mailto:static.void....@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
