Hello, I would like to add a warning to the lvmcache man page about its suitability in environments that expect unclean shutdowns. I've been using lvmcache on my laptop which has a small nvme drive and a much larger hdd. I am using approx 60GiB of the nvme drive as a cache for the 1TiB HDD. With both "writethrough" and "writeback" modes an unclean shutdown results in the entire cache being marked as dirty. On next boot the system then spends a long time (4+ hours) writing the cache out to disk. From what I can see this is known behavior of lvmcache ([1] and [2]). It's even documented in the kernel device mapper docs [3]. It seems to me that dm-cache and lvmcache are not appropriate for environments that expect unclean shutdowns. In those environments I have found bcache to be a bit more robust. This is not a criticism of lvmcache and dm-cache. I am sure they perform well in more robust environments. But I wonder if it would be appropriate to add a warning note to the lvmcache man page about this issue? I am using Ubuntu 20.04 currently, if that's relevant, and I saw the same issue with 18.04. 1: https://www.redhat.com/archives/dm-devel/2019-July/msg00114.html 2: https://www.redhat.com/archives/dm-devel/2014-December/msg00143.html 3: https://github.com/torvalds/linux/blame/79dede78c0573618e3137d3d8cbf78c84e25fabd/Documentation/admin-guide/device-mapper/cache.rst#L140-L143 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
