Hi, I recently set up dm-cache below my main LVM, so that /dev/md2 (a RAID-0 of two SSDs) has an LVM with /dev/mapper/cache-blocks and /dev/mapper/cache-metadata, which then back /dev/md1 (a RAID-6 of rotating disks), where my main LVM, including the root device etc., lies. After a fair amount of fighting with udev and initramfs-tools, plus upping the block size to 2048 since 512 complained about not enough RAM (on a 24GB machine!), this seems to boot up and work, but I seem to get absolutely zero cache hits. dmsetup table for the device: cache: 0 23440891904 cache 254:0 254:1 9:1 2048 1 writeback default 4 random_threshold 8 sequential_threshold 512 dmsetup status for it: cache: 0 23440891904 cache 913/8192 0 170976 0 9614 0 0 0 0 0 2 migration_threshold 2048 4 random_threshold 8 sequential_threshold 512 Note in particular 0/170976 cached reads and 0/9614 cached writes. Is this normal? Is there any good reason why an LVM on top of a dm-cache device would not be supported? Or do I just need to wait a few more hours/weeks/days until it starts being aggressive? /* Steinar */ -- Homepage: http://www.sesse.net/ -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
