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. > The other day I was benchmarking lvmcache (on CentOS 7.2), but I couldn't get it to give much advantage for writeback caching use case.. even when I was using fast nvme/pcie cache device. It just wouldn't cache writes properly for me. I tried both the smq and mq, and played with all of the parameters.. it just wouldn't help much for my use case. YMMV. > 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
