On Thu, Oct 24, 2019 at 05:21:04PM +0200, Daniel Kiper wrote: > On Thu, Oct 24, 2019 at 04:43:58AM +0000, Michael Chang wrote: > > On Wed, Oct 23, 2019 at 12:48:23PM +0200, Daniel Kiper wrote: > > > On Wed, Oct 16, 2019 at 06:15:30AM +0000, Michael Chang wrote: > > > > The lvm cache logical volume is the logical volume consisting of the > > > > original and the cache pool logical volume. The original is usually on a > > > > larger and slower storage device while the cache pool is on a smaller > > > > and faster one. The performance of the original volume can be improved > > > > by storing the frequently used data on the cache pool to utilize the > > > > greater performance of faster device. > > > > > > > > The default cache mode "writethrough" ensures that any data written will > > > > be stored both in the cache and on the origin LV, therefore grub can go > > > > straight to read the original lv as no data loss is guarenteed. > > > > > > > > The second cache mode is "writeback", which delays writing from the > > > > cache pool back to the origin LV to have increased performance. The > > > > drawback is potential data loss if losing the associated cache device. > > > > > > > > During the boot time grub reads the LVM offline i.e. LVM volumes are not > > > > activated and mounted, IMHO it should be fine to read directly from > > > > original lv since all cached data should have been flushed back in the > > > > process of taking it offline. > > > > > > Is it possible to enforce all GRUB writes to the original device instead > > > of cache during installation process? > > > > I couldn't give concrete answer whether it is possible, but it sounds to > > me not good idea because in general bypassing the cache could > > potentially break the consistency of data and the data being cached. > > > > Perhaps some system calls could help to sync the data out of the lvm > > cache to the original LV during installation process. It seems fsync > > does it for us, but I didn't have good idea either if it is enough. > > May I ask you to investigate that and if it is needed add required > install code. I mean fsync(), etc.
Sure. And please bear with me if it takes long to answer as other task was sidetracking. Thanks, Michael > > Daniel > > _______________________________________________ > Grub-devel mailing list > Grub-devel@gnu.org > https://lists.gnu.org/mailman/listinfo/grub-devel _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
