Am 24.12.2015 um 15:56 schrieb Piotr Pawłow: > Hello, >> - both hdd and ssd in one LVM VG >> - one LV on each hdd, containing a btrfs filesystem >> - both btrfs LV configured as RAID1 >> - the single SDD used as a LVM cache device for both HDD LVs to speed up >> random access, where possible > > I have a setup like this for my /home. It works but it's a crappy solution. > Indeed? Exactly like this? Great to hear. But sad to hear it is not a good solution. > The effective capacity for caching is halved, and it takes twice as much > time to fully cache your working set, because you get a cache miss at > least once for each mirror. > > There are also some gotchas: > > - you should use "device=" mount options, or else there is a danger of > btrfs mounting origin devices and even mixing cached and origin in one > FS. I completely broke my FS before realizing what's going on. Hmm, strange. I thought btrfs should not even know of the lvmcache. It would just try to mount the HDD LVs and the caching is done automatically via lvmcache? > - you should use writethrough mode if you only have one SSD. There was a > bug in LVM where it wouldn't save the caching mode and revert to > writeback after restart, so make sure you use the latest version of LVM > tools. Do you know, which version is good? > - if your SSD dies, you may have to use vgcfgbackup, manual config edit, > then vgcfgrestore to remove the cache, because last time I checked, LVM > tools still were handling writethrough cache the same as writeback, > disallowing volume activation without the cache and removal of missing > cache. > Sounds complicated, but possible. Pity that LVM does not auto-remove the cache if it is not there... > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" 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-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
