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From Yan Chunlu <>
Subject Re: do I need to add more nodes? minor compaction eat all IO
Date Mon, 25 Jul 2011 12:59:55 GMT
I am using normal SATA disk,  actually I was worrying about whether it
is okay if every time cassandra using all the io resources?
further more when is the good time to add more nodes when I was just
using normal SATA disk and with 100r/s it could reach 100 %util....

how large the data size it should be on each node?

below is my iostat -x 2 when doing node repair, I have to repair
column family separately otherwise the load will be more crazy:

Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s
avgrq-sz avgqu-sz   await r_await w_await  svctm  %util
sda               1.50     1.50  121.50   14.00     3.68     0.30
60.19   116.98 1569.46   59.49 14673.86   7.38 100.00

On Sun, Jul 24, 2011 at 8:04 AM, Jonathan Ellis <> wrote:
> On Sat, Jul 23, 2011 at 4:16 PM, Francois Richard <> wrote:
>> My understanding is that during compaction cassandra does a lot of non sequential
readsa then dumps the results with a big sequential write.
> Compaction reads and writes are both sequential, and 0.8 allows
> setting a MB/s to cap compaction at.
> As to the original question "do I need to add more machines" I'd say
> that depends more on whether your application's SLA is met, than what
> % io util spikes to.
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of DataStax, the source for professional Cassandra support

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