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Posted to user@cassandra.apache.org by Kevin Burton <bu...@spinn3r.com> on 2014/11/26 02:31:49 UTC
RAM vs SSD for real world performance?
The new SSDs that we have (as well as Fusion IO) in theory can saturate the
gigabit ethernet port.
The 4k random read and write IOs they’re doing now can easily add up quick
and they’re faster than gigabit and even two gigabit.
However, not all of that 4k is actually used. I suspect that on average
half is wasted.
But the question is how much. Of course YMMV.
I’m thinking of getting our servers with a moderate amount of RAM. Say
24GB. Then allocate 8GB to Cassandra, another 8GB to random daemons we
run, then another 8GB to page cache.
Curious what other people have seen here in practice. Are they getting
comparable performance to RAM in practice? Latencies would be higher of
course but we’re fine with that.
--
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Location: *San Francisco, CA*
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Re: RAM vs SSD for real world performance?
Posted by Kevin Burton <bu...@spinn3r.com>.
I imagine I’d generally be happy if we were CPU bound :-) … as long as the
number of transactions per second is generally reasonable.
On Tue, Nov 25, 2014 at 7:35 PM, Robert Coli <rc...@eventbrite.com> wrote:
> On Tue, Nov 25, 2014 at 5:31 PM, Kevin Burton <bu...@spinn3r.com> wrote:
>
>> Curious what other people have seen here in practice. Are they getting
>> comparable performance to RAM in practice? Latencies would be higher of
>> course but we’re fine with that.
>>
>
> My understanding is that when one runs Cassandra with SSDs, one replaces
> the typical i/o bound with a CPU bound. Cassandra also has various internal
> assumptions that do not make best use of the spare i/o available;
> SSD+Cassandra has only been deployed at scale for a few years, so this
> makes sense.
>
> =Rob
>
>
--
Founder/CEO Spinn3r.com
Location: *San Francisco, CA*
blog: http://burtonator.wordpress.com
… or check out my Google+ profile
<https://plus.google.com/102718274791889610666/posts>
<http://spinn3r.com>
Re: RAM vs SSD for real world performance?
Posted by Robert Coli <rc...@eventbrite.com>.
On Tue, Nov 25, 2014 at 5:31 PM, Kevin Burton <bu...@spinn3r.com> wrote:
> Curious what other people have seen here in practice. Are they getting
> comparable performance to RAM in practice? Latencies would be higher of
> course but we’re fine with that.
>
My understanding is that when one runs Cassandra with SSDs, one replaces
the typical i/o bound with a CPU bound. Cassandra also has various internal
assumptions that do not make best use of the spare i/o available;
SSD+Cassandra has only been deployed at scale for a few years, so this
makes sense.
=Rob