Google云端Bigtable耐用性/可用性保证(Google Cloud Bigtable Durability/Availability Guarantees)

 我希望Google的某人提供有关Cloud Bigtable服务提供的耐用性和可用性保证的一些准则。 
 
 这是我迄今为止的理解： 
 
 
 
 最小群集需要3个节点的事实表明，至少在一个区域内，数据非常耐用并且被复制到3个节点。 
 
 
 然而，Google员工的这种回答表明，“Cloud Bigtable不会复制数据” - 与Cloud Bigtable主页上的报价直接矛盾，并声称其“采用复制存储策略”。 那它是哪一个？ 它是否被复制？ 如果是这样，保留多少份？ 
 
 
 群集只能在特定区域内建立的事实表明群集的可用性直接与该区域的可用性紧密相关。 因此，如果我想拥有一个高度可用的基于Bigtable的数据存储，最好的做法是跨多个区域设置独立的群集，并自行处理跨群集的写入同步？ 
 
 
 没有关于跨区域的Bigtable集群是否独立的信息。 如果我要在多个区域建立集群，并且一个区域关闭，我们能否期望其他区域的集群继续工作？ 或者是否存在一些潜在的单点故障，甚至可能跨区域影响集群？ 
 
 与对这些细节非常具体的App Engine数据存储区相比，Cloud Bigtable文档相当缺乏，或者至少我没有设法找到详细介绍这些方面的页面。 
 
 Cloud Bigtable文档在其他方面同样模糊，例如在值的大小限制方面， 文档指出单个值应该保持在“每个单元约10 MB”以下。 “〜10 MB”是什么意思？！ 我是否可以硬编码10MB的限制，并期望它始终能够正常工作，或者每天都会因为未知因素而发生变化？ 
 
 无论如何，如果我听起来很激动，请道歉。 我真的很想使用Bigtable服务。 但是，我想，像其他很多人一样，在能够投资它之前，需要了解它的耐用性/可用性方面。 谢谢。 

I would like someone from Google to provide some guidelines on the durability and availability guarantees provided by the Cloud Bigtable service.
 
Here is my understanding so far:
 
 
 
The fact that the minimum cluster requires 3 nodes suggests that, at least within a zone, the data is highly durable and replicated to 3 nodes.
 
 
However, this answer by a Googler states that "Cloud Bigtable doesn’t replicate data" — directly contradicting the quote on the Cloud Bigtable homepage which claims it "is built with a replicated storage strategy". So which is it? Is it replicated or not? And if so, how many copies are kept?
 
 
The fact that clusters can only be set up within a particular zone suggests that the availability of a cluster is tied directly to the availability of that zone. So if I want to have a highly available Bigtable-based data storage, would it be best practice to set up independent clusters across multiple zones and handle the synchronisation of writes across the clusters myself?
 
 
There is no information on whether Bigtable clusters across zones are independent or not. If I were to set up clusters across multiple zones, and one zone goes down, could we expect the clusters in other zones to carry on working? Or is there some underlying single point of failure which could impact clusters even across zones?
 
Compared to the App Engine datastore which is very specific about these details, the Cloud Bigtable documentation is rather lacking — or, at least, I've not managed to find a page which goes into detail on these aspects.
 
The Cloud Bigtable docs are similarly vague on other aspects, e.g. on the matter of size limits for values, the documentation states that individual values should stay below "~10 MB per cell". What on earth does "~10 MB" mean?! Can I hardcode a limit of exactly 10MB and expect it to always work or will that change from day to day dependent on unknown factors?
 
Anyway, apologies if I sound agitated. I genuinely would like to use the Bigtable service. But I, like presumably many others, need to understand the durability/availability aspects of it before being able to invest in it. Thank you.

原文：https://stackoverflow.com/questions/30757561