But in my new configuration backing device is a bare disk, no LVM, caching device is on LVM though. - Pradeep Jindal On Tue, Mar 29, 2016 at 1:49 AM, Vojtech Pavlik <vojtech@xxxxxxxx> wrote: > On Tue, Mar 29, 2016 at 01:35:32AM +0530, Pradeep Jindal wrote: > >> > > I am facing a weird problem, I earlier had a configuration wherein my >> > > backing device was a logical volume (LVM) backed by 3 software RAID0 >> > > arrays having 2x1TB disks each, so totally 6TB of storage for backing >> > > device and 300GB logical volume (LVM) backed by SSD as a caching >> > > device. Both were configured as a cache set and I was getting around >> > > 84% cache hit ratio. >> > > >> > > Now, I have changed the backing device to a bare (no LVM, no raid) 6TB >> > > disk while everything else stays same (caching device on LVM, 300GB) >> > > and for exactly same workload I am only getting 58-60% cache hit >> > > ratio. >> > > >> > > I am confused, what could be the reason? >> > >> > Full stripe size writes are configured according to the backing device, >> > for example. > >> Didn't quite get it, could you please elaborate? > > Backing devices that advertise a stripe size cause bcache to enable a > mode where it tries to always write a full stripe to the backing > devices, hence changing behavior of the cache. > > -- > Vojtech Pavlik > Director SuSE Labs -- 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
