On Wed, Dec 15, 2010 at 4:05 PM, Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > On 12/15/2010 03:26 PM, luvar@xxxxxxxxxxxx wrote: >> >> Hi, >> Iam new in problematic of caching persistent data. I want to use caching >> (on ssd disk) on my desktop with a lot of ram. I hope, it will provide me >> better latency for starting programs (developer/scientific desktop). My >> questions are: >> >> Is it possible to use single ssd disk for making two caches? One for >> /dev/md2 (root partition, raid10) and second for /dev/md3 (raid5,home >> partition, etc) (I hope this is possible by partitioning that ssd disk and >> using partitions for caching) > > Yep. One cache device can be used with (currently) up to 256 backing > devices. > >> >> Is it dangerous (in terms of data loss) to use writethrough caching to >> single ssd disk of raid5 block device? (I have 5 disks, using lvm on top of >> raid). > > Shouldn't be, recovery from unclean shutdown is quite well tested, both > writethrough and writeback should be perfectly safe. > >> >> For caching device is most critical number for random reads or operations >> per second. Is it right? > > For writethrough caching random reads, for writeback both reads and writes. > >> >> Trim is not need feature for cache ssd device. It will have same cache >> performance without it. Is it right? > > Really just depends on the ssd; some (cheaper, earlier) drives are known for > performance significantly degrading over time, with trim helps with (but > doesn't necessarily eliminate). Bcache uses trim if it's available. > >> >> What benefits/disadvantages have bcache [1] project over dm-cache [2] and >> flashcache [3]? My current knowledge is that writethrough is possible only >> in bcache, but dm-cache is implemented in more "standard" way (thdough >> devicemaper). Also bcache has some more information on web. >> >> [1] - http://bcache.evilpiepirate.org/ >> [2] - http://users.cis.fiu.edu/~zhaom/dmcache/index.html >> [3] - https://github.com/facebook/flashcache > > Flashcache is based off of dm-cache. > > Flashcache has been used in production awhile, bcache is still a little > rough around the edges - but bcache has better performance, more features, > and it always orders writes correctly so as to be crash safe (flashcache has > a "torn write" problem). Kent, now that we are on the topic, I wonder if there has been some benchmarking comparing bcache to flashcache performance? Also I wonder if you plan to target for getting bcache included in mainline kernel. I wonder if such attempts were made for flashcache but that's probably off-topic. Thanks. -- Nauman > >> >> PS: Is there any tutorial for gentoo users? > > Nah, I'm an ubuntu/debian user. For caching / the important thing is to hook > into your initramfs and get everything loaded before you mount your root > filesystem. > >> >> Thanks for any explanations / answers, >> -- >> LuVar >> -- >> 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 > > -- > 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 > -- 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
