On 2017/9/11 下午4:04, FERNANDO FREDIANI wrote: > Hi folks > > In Bcache people normally use a single SSD for both Read and Write > cache. This seems to work pretty well, at least for the load we have > been using here. > > However in other environments, specially on ZFS people tend to suggest > to use dedicated SSDs for Write (ZIL) and for Read (L2ARC). Some say > that performance will be much better in this way and mainly say they > have different wearing levels. > The issue now a days is that SSDs for Write Cache (or Writeback) don't > need to have much space available (8GB normally is more than enough), > just enough for the time until data is committed to the pool (or > slower disks) so it is hard to find a suitable SSD to dedicate to this > propose only without overprovisioning that part. > On the top of that newer SSDs have changed a lot in recent times using > different types of memory technologies which tend to be much durable. > > Given that I personally see that using a single SSD for both Write and > Read cache, in any scenarios doesn't impose any significant loss to > the storage, given you use new technology SSDs and that you will > hardly saturate it most of the time. Does anyone agree or disagree > with that ? Hi Fernando, If there is any real performance number, it will be much easier to response this idea. What confuses me is, if user reads a data block which is just written to SSD, what is the benefit for the separated SSDs. Yes I agree with you that some times a single SSD as cache device is inefficient. Multiple cache device on bcache is a not-implemented yet feature as I know. Thanks. -- Coly Li -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
