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From Soerian Lieve <sli...@liveramp.com>
Subject Re: Reduced write performance when reading
Date Fri, 24 Jul 2015 20:55:31 GMT
I was on CFQ so I changed it to noop. The problem still persisted however.
Do you have any other ideas?

On Thu, Jul 23, 2015 at 5:00 PM, Jeff Ferland <jbf@tubularlabs.com> wrote:

> Imbalanced disk use is ok in itself. It’s only saturated throughput that’s
> harmful. RAID 0 does give more consistent throughput and balancing, but
> that’s another story.
>
> As for your situation with SSD drive, you can probably tweak this by
> changing the scheduler is set to noop, or read up on
> https://www.kernel.org/doc/Documentation/block/deadline-iosched.txt for
> the deadline scheduler (lower writes_starved value). If you’re one CFQ,
> definitely ditch it.
>
> -Jeff
>
> On Jul 23, 2015, at 4:17 PM, Soerian Lieve <slieve@liveramp.com> wrote:
>
> I set up RAID0 after experiencing highly imbalanced disk usage with a JBOD
> setup so my transaction logs are indeed on the same media as the sstables.
> Is there any alternative to setting up RAID0 that doesn't have this issue?
>
> On Thu, Jul 23, 2015 at 4:03 PM, Jeff Ferland <jbf@tubularlabs.com> wrote:
>
>> My immediate guess: your transaction logs are on the same media as your
>> sstables and your OS prioritizes read requests.
>>
>> -Jeff
>>
>> > On Jul 23, 2015, at 2:51 PM, Soerian Lieve <slieve@liveramp.com> wrote:
>> >
>> > Hi,
>> >
>> > I am currently performing benchmarks on Cassandra. Independently from
>> each other I am seeing ~100k writes/sec and ~50k reads/sec. When I read and
>> write at the same time, writing drops down to ~1000 writes/sec and reading
>> stays roughly the same.
>> >
>> > The heap used is the same as when only reading, as is the disk
>> utilization. Replication factor is 3, consistency level on both reads and
>> writes is ONE. Using Cassandra 2.1.6. All cassandra.yaml settings set up
>> according to the Datastax guide. All nodes are running on SSDs.
>> >
>> > Any ideas what could cause this?
>> >
>> > Thanks,
>> > Soerian
>>
>>
>
>

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