>>>>> "Ram" == Ram Ramesh <rramesh2400@xxxxxxxxx> writes: Ram> On 03/06/2016 07:58 PM, John Stoffel wrote: Ram> Any one here actually use SSD caches for RAID arrays? Can you Ram> share your experience and let me know your choice of the type of Ram> cache methods your tired/used and why you think one is better or Ram> worse than other? If it is possible, please provide raid Ram> type/size and ssd size used. >> >> I'm using a pair of 4Tb drives mirrored, and a pair of 512gb SSDs, >> also mirrored, along with lvmcache to setup my caching across a couple >> of volumes. >> >> I honestly haven't seen huge improvements, but I also haven't had the >> time to do any serious testing either. Whcih I should do. I've been >> sorta thinking that using the Phoronix testing stuff would be the way >> to go. >> >> My SSDs and 4Tb drives are all on an LSI 8-port SATA controller, PCI-E >> 4x I think. It's an MPT SAS-2 controller. I did this so that my boot >> drives are some partitions on the SSDs, and then I use two more >> mirrored partitions for the cache. >> >> And this is an NFS server for my home directories, etc. >> >> I didn't use bcache because you can't remove a cache device without >> rebooting, or at least bringing a device offline and back online, >> which doesn't fit my desires to be able to dynamically add/remove >> caches, esp for the testing I've never bothered to do. >> >> John Ram> I do not have lvm, but already have a live (regular) file Ram> system. While I can accept downtime, I cannot accept formatting Ram> drives/disks. I simply do not have the extra space to copy back Ram> and forth. That is why I thought of dmcache. I ran a fio Ram> experiment on my ssd (old curial M4) and I am getting 6K (random) Ram> IOPs whereas my raid gives me about 1.5K. I really do not see Ram> much point unless my new SSD puts out some decent numbers stand Ram> alone. I'm not sure fio is the right test here, but it all depends on what you do, which is the curse of performance testing! I kinda like kernel compiles, and doing lots of image viewing (building of thumbnails, etc) to see how things will speed up in my common usecase. Ram> Thanks for sharing the details of your setup. Good luck with your testing, I'd love to see your results when you've decided which way to go. -- 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
