This is a good observation. On Thu, Oct 4, 2012 at 5:39 AM, Andrew Purtell <[email protected]> wrote:
> 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 <[email protected]> > 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> 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 > >> > > >> >
