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From Andrew Purtell <apurt...@apache.org>
Subject Re: zookeeper on SSD
Date Thu, 04 Oct 2012 04:39:22 GMT
Even so, I've seen in notes from attendees of Amazon's "DynamoDB For
Developers" talks that Amazon says they found it necessary to work
"extensively" with their SSD vendor (not stated publicly AFAIK) to
engineer out latency spikes. I'd imagine they started with a strong
vendor and not a low end device, but of course this is just
speculation.

On Thu, Oct 4, 2012 at 12:28 PM, Ted Dunning <ted.dunning@gmail.com> wrote:
> Yes.
>
> And Patrick's experience is not unexpected.  There is, however, a huge
> variation with different types of flash memory.  The software driving the
> flash can also result in very different experience.  The experiences that
> he alludes to are likely with a conventional SSD packaging of flash driven
> via the normal block device emulator.  That can be substantially
> sub-optimal, depending on which vendor and configuration you use.
>
> On Thu, Oct 4, 2012 at 5:12 AM, Jun Rao <junrao@gmail.com> wrote:
>
>> Patrick,
>>
>> Thanks for the info. Does each ZK write wait for log being flushed to disk?
>>
>> Jun
>>
>> On Wed, Oct 3, 2012 at 6:13 PM, Patrick Hunt <phunt@apache.org> wrote:
>>
>> > My experience with SSDs and ZK has been discouraging. SSDs have some
>> > really terrible corner cases for latency. I've seen them take 40+
>> > seconds (that's not a mistake - seconds) for fsync to complete. When
>> > this happened (every few hours) all of the sessions would timeout.
>> >
>> > See this article:
>> > http://storagemojo.com/2012/06/07/the-ssd-write-cliff-in-real-life/
>> >
>> > Patrick
>> >
>> > On Wed, Oct 3, 2012 at 9:59 AM, Jun Rao <junrao@gmail.com> wrote:
>> > > Hi,
>> > >
>> > > Will storing the ZK commit log on SSD improve ZK write latency? Does a
>> ZK
>> > > write wait until data is flushed to disk?
>> > >
>> > > Thanks,
>> > >
>> > > Jun
>> >
>>

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