First of all, I would like to thanks for answers. One more question and some reply in text. After making ssd disc a cache for some partition, there is possibility to detach cache. What should I do to "erase" (trim) whole disk for another benchmarking? I think that "dd if=/dev/zero of=/dev/sdx" wouldnt be right command. ----- "Nauman Rafique" <nauman@xxxxxxxxxx> wrote: > 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. I hope, next two links will help in making comparison. http://www.mysqlperformanceblog.com/2010/05/10/flashcache-first-experiments/ http://www.mysqlperformanceblog.com/2010/05/18/flashcache-more-benchmarks/ There is simple methodology of cache testing by using it with mysql database. I hope, someone will catch this discussion and try some comparable test on bcache. For me will be next test sufficient: Activate caching and make for example 20 reboots. Measure time from computer bios beep till starting gimp, which will be in gnome/kde/fluxbox autostart script. Of course before starting gimp, there will be need for starting some other programs like firefox, eclipse, mplayer with some film... I would like to see these times of booting in graph. I promise that after installation of bcache I will do this test with bcache and post it here. > > 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 Âhttp://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 Âhttp://vger.kernel.org/majordomo-info.html > > PS: I am now decided to use bcache (after buying some ssd). -- 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
