Raid 1 is going to slow down the writes, but it's probably still a big win over write-through mode. Of course raid 1 isn't invincible, and you can still get silent data corruption on the devices. I'm sure there's still some nasty bugs somewhere in bcache writeback mode that we haven't found yet. They should be rare, and you might not encounter them, but I'd be leary of putting anything too valuable on writeback devices. If things go wrong, recovery can be extremely difficult. Caveat emptor, but if you do try it please let everyone know how it works for you. Adam On Fri, Apr 20, 2012 at 10:05 AM, Roberto Alcântara <roberto@xxxxxxxxxxxxxx> wrote: > Adam, > > What about use bache in raid1 flash devices? > > - Roberto > > > On Fri, Apr 20, 2012 at 1:53 PM, Adam Berkan <aberkan@xxxxxxxxxx> wrote: >> If you completely lose a flash device that contains significant >> quantities of dirty data, you'll have a hard time recovering any data >> from the backing device. All of the writeback testing we've done so >> far has assumed device failures are limited to small regions of the >> device, and bcache tries to recover what it can when it encounters >> such errors. It doesn't do anything reasonable in the case of full >> device loss. >> >> I would not recommend using bcache in writeback mode anywhere where >> you can't afford to lose the whole device. >> >> Adam >> >> On Fri, Apr 20, 2012 at 8:51 AM, Brad Campbell <brad@xxxxxxxxxxxxxxx> wrote: >>>> >>> On 17/04/2012, at 4:30 PM, Kent Overstreet <koverstreet@xxxxxxxxxx> wrote: >>> >>>> >>>> >>>>> Also ... do you think that your code is production ready when using bcache >>>>> to do writeback caching ? Of course I will keep testing but I'd like to >>>>> know if you think the code by now is production ready. >>>> >>>> Yeah, it is. Test it on your configuration, etc. etc. but writeback is >>>> pretty mature and well tested at this point. >>>> >>> I've been giving serious thought to using this in a production environment. It performs well in my staging system, but my biggest concern revolves around the ultimate reliability of the ssd. >>> >>> How much testing have you performed with regard to cache device failures in a writeback scenario? I like the idea of mirroring the cache devices to replicate dirty data, however I know that is not implemented yet. >>> >>> We run a raid10 of SAS cheetahs. I'd love to mount a cache in there, but ultimately we have little information about what happens if the ssd starts to flake out. I guess more than that, there is little real information out there detailing common or potential ssd failure modes. >>> >>> I'd assume you've performed plenty of testing over the development of bcache. Can you fill us in a bit as to what to expect when things go south? >>> >>> Regards, >>> Brad-- >>> 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
