On 16 August 2012 02:23, Dave Jiang <dave.jiang@xxxxxxxxx> wrote: > On 08/15/2012 04:51 AM, John McCabe-Dansted wrote: >> On Wed, Aug 15, 2012 at 7:30 PM, C Sights <csights@xxxxxxxxxxx> wrote: >>> Hi all, >>> Has anyone tried creating a bcache device in RAM and benchmarking >>> performance of that versus just allowing that RAM to be used as file system >>> buffers? >> I doubt it; bcache is designed to use non-volatile flash memory rather >> than ram. >> >> If the filesystem is readonly, I imagine that using RAM for bcache >> would lead to worse performance as it would just add overhead. If the >> filesystem is read-write then it might lead to better performance but >> would also lead to the file-system being trashed on if unexpected >> power loss occurs. >> >> Under what circumstance would you intend to actually use ram backed bcache? >> > > So the Intel Xeon E5-2600 series platforms has this feature called > asynchronous DRAM refresh (ADR). Essentially it's battery backed DRAM on > per DIMM socket basis. I have written a RAM disk driver on top of that > experimentally and played a little bit with it used by bcache instead of > SSD. Writing to the memory region isn't going to be as fast as normal > cached RAM because you have to ensure the data is flushed to the DRAM. > However, read should be the same as cached DRAM. But the writing should > still be faster than SSD. Anyhow, I'm more curious as to how I can > benchmark this to demonstrate if this is a benefit with bcache. i.e. > what benchmarking tool(s) I should use and with what parameters etc. fio - the flexible I/O tester is by far the best tool. It's usage is demonstrated on the bcache wiki frontpage and there are numerous tutorials. I suggest using the linux AIO engine and a high queue depth to see the benefit. > > -- > 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 Joseph. -- CTO | Orion Virtualisation Solutions | www.orionvm.com.au Phone: 1300 56 99 52 | Mobile: 0428 754 846 -- 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
