On Wed, 10 Jun 2015 16:59:10 -0700 Ming Lin <mlin@xxxxxxxxxx> wrote: > On Wed, Jun 10, 2015 at 4:00 PM, Neil Brown <neilb@xxxxxxx> wrote: > > On Wed, 10 Jun 2015 15:27:07 -0700 > > Ming Lin <mlin@xxxxxxxxxx> wrote: > > > >> Hi NeilBrown, > >> > >> As you may already see, I run a lot of tests with 10 HDDs for the patchset > >> "simplify block layer based on immutable biovecs" > >> > >> Here is the summary. > >> http://minggr.net/pub/20150608/fio_results/summary.log > >> > >> MD RAID6 read performance is OK. > >> But write performance is much lower than HW RAID6. > >> > >> Is it a known issue? > > > > It is not unexpected. > > There are two likely reasons. > > One is that HW RAID cards often have on-board NVRAM which is used as a > > write-behind cache. This allows better throughput by hiding latency and more > > often gathering full-stripe writes. HW RAID cards may also have accelerators > > for the parity calculations, but that is not likely to make a big difference. > > What sort of RAID6 controller do you have? > > PERC H730 Mini http://www.dell.com/learn/us/en/04/campaigns/dell-raid-controllers 1GB NV Flash Backed Cache on the H730 That would explain a lot of performance difference for writes. NeilBrown -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
