On Wed, Feb 10, 2016 at 05:21:51PM -0500, John Stoffel wrote: > >>>>> "Pasi" == Pasi Kärkkäinen <pasik@xxxxxx> writes: > > Pasi> On Mon, Feb 08, 2016 at 10:34:09AM -0500, John Stoffel wrote: > >> > Thomas> I'm planning on setting up a dual raid5 array for hosting vm's > Thomas> off LVM, I would like to add an ssd cache to help with typical > Thomas> server system loads, and some mixed read/write loads for game > Thomas> servers. > >> > Thomas> I'm wondering what the "best" route for me to go is. There's a > Thomas> few options that I know of, like flashcache, dm-cache, and > Thomas> bcache. The question is which of those is better suited to my > Thomas> use case? > >> > >> I looked into both bcache and lvmcache and went with lvmcache because > >> it made more sense to me. But one restriction is that the cache LVs > >> must be in the same VGs as the volume to cache. So you might need to > >> partition your SSD(s) and put the partitions into seperate VGs so that > >> you can cache one or more LVs. > >> > >> I'm using it at home to cache a RAID1 4tb VG, with a pair of mirrored > >> SSDs. I'm a big believer in mirroring, esp for critical stuff like > >> this. > >> > >> Unfortunately, I don't have a good performance measurements of how > >> much help this actually gives me. It *feels* faster, but since I > >> don't have before/after measurements, I could just have wasted a bunch > >> of money. > >> > >> So I'd recommend lvmcache overall, since it does seem to help, but > >> push for better performance metrics and measurement. Heh, maybe it's > >> time for me to start writing up lvmcachetop to help measure things. > > Pasi> The other day I was benchmarking lvmcache (on CentOS 7.2), but I > Pasi> couldn't get it to give much advantage for writeback caching use > Pasi> case.. even when I was using fast nvme/pcie cache device. > > What were you using? I should spin up fio and see what I can > find... or maybe even just some kernel compiles, image manipulation, > etc. > Yeah I was benchmarking small random 4 kB writes, using fio. iodepth=64 and jobs=12. > Let's see what we can come up with for benchmarking, since it would be > a big help! I'm running kernel 4.4-rc7 right now on a Debian Jessie system. > > Pasi> It just wouldn't cache writes properly for me. I tried both the > Pasi> smq and mq, and played with all of the parameters.. it just > Pasi> wouldn't help much for my use case. > > I have both mq and smq compiled into the kernel, so I can't figure out > how to change between them to test. > Hmm, yeah, I think it was documented on the lvmcache man page. I can't check my notes right now.. > John -- Pasi -- 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
