No, doesn't' work either i'm afraid. Below is example of failing silently with ram disk and succeeded with HDD as cache device. Tested with /lib/modules/4.5.0-rc3+/kernel/drivers/md/bcache/bcache.ko with zram - doesn't work ================= $ ls -al /sys/fs/bcache/ total 0 drwxr-xr-x 2 root root 0 Feb 25 13:42 . drwxr-xr-x 9 root root 0 Feb 25 13:40 .. --w------- 1 root root 4096 Feb 25 13:40 register --w------- 1 root root 4096 Feb 25 13:40 register_quiet $ file /dev/zram0 /dev/zram0: block special (250/0) $ fdisk -l /dev/zram0 Disk /dev/zram0: 1 GiB, 1073741824 bytes, 262144 sectors $ make-bcache -C /dev/zram0 UUID: 87e63981-7bd8-4cc3-93db-9ca275367c21 Set UUID: 0bba8852-ad4f-41f4-bfa3-679a886a14ad version: 0 nbuckets: 2048 block_size: 8 bucket_size: 1024 nr_in_set: 1 nr_this_dev: 0 first_bucket: 1 No errors, but nothing in dmesg and contents of /sys/fs/bcache/ remain exactly the same... no UUID. Seems to just silently fail. with HDD - works as expected. ===================== $ fdisk -l /dev/sdf Disk /dev/sdf: 1 GiB, 1073741824 bytes, 2097152 sectors $ file /dev/sdf /dev/sdf: block special (8/80) $ make-bcache -C /dev/sdf UUID: 3234c9e7-8186-4a7c-99a8-ae6a371c6f2c Set UUID: 9a71faf7-a408-4f4d-906e-e5d67e43291f version: 0 nbuckets: 2048 block_size: 1 bucket_size: 1024 nr_in_set: 1 nr_this_dev: 0 first_bucket: 1 $ ls -al /sys/fs/bcache/ total 0 drwxr-xr-x 3 root root 0 Feb 25 13:48 . drwxr-xr-x 9 root root 0 Feb 25 13:40 .. drwxr-xr-x 7 root root 0 Feb 25 13:48 9a71faf7-a408-4f4d-906e-e5d67e43291f --w------- 1 root root 4096 Feb 25 13:40 register --w------- 1 root root 4096 Feb 25 13:40 register_quiet $ dmesg [ 714.168488] bcache: register_cache() registered cache device sdf Thank you. On 24 February 2016 at 15:37, Eric Wheeler <lists@xxxxxxxxxxxx> wrote: > > On Tue, 16 Feb 2016, Scott McGillivray wrote: > >> Hello >> >> I am using Ubuntu 15.10 with latest nightly 4.5 kernel. Ubuntu creates >> 16 RAM drives as /dev/ram0 - ram16 by default and i am trying to test >> bcache and use one of these as a cache device. >> >> wipefs /dev/sdd >> wipefs /dev/sdd -a >> wipefs /dev/ram0 >> wipefs /dev/ram0 -a >> make-bcache -B /dev/sdd -C /dev/ram0 > > Does it work with /dev/zram0? You would prep it something like this: > > modprobe zram > echo $((1024*1024*1024)) > /sys/block/zram0/disksize # 1GB > make-bcache -C /dev/zram0 > > -Eric > > > >> At this point there were no errors output but there is also no UUID >> entry in /sys/fs/bcache/. Only register and register_quiet. >> >> bache-super-show correctly prints info about both block and cache >> devices when queried but when i try to manually attach the cache >> device with echo cset.uuid > /sys/block/bcache0/bcache/attach i get no >> error but in dmesg i see >> >> bcache: __cached_dev_store() Can't attach >> 3f2521a6-2103-4e2e-a47d-cc56558e8f7d: cache set not found >> >> If i repeat this example but use another sd block device as cache then >> it works OK. >> >> Can anyone confirm if it should be possible to use the ramdisk based >> block device as a caching device with bcache ? >> >> I also tried to use a loop device as cache and that didn't work >> either.. i got "kernel bug" in dmesg for >> drivers/md/bcache/super.c:1812. RIP [] >> cache_alloc.isra.21+0x646/0x670[bcache] >> >> Does bcache need the cache device to be a certain block type i.e sd 8 >> ? Should i be able to use any block device from /proc/devices as a >> cache device ? >> >> The kernel options used for ramdisk are: >> >> CONFIG_BLK_DEV_RAM=y >> CONFIG_BLK_DEV_RAM_COUNT=16 >> CONFIG_BLK_DEV_RAM_SIZE=65536 >> CONFIG_BLK_DEV_RAM_DAX=y >> >> Thank you. >> Scott >> -- >> 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 >> > > > > -- > Eric Wheeler, President eWheeler, Inc. dba Global Linux Security > 888-LINUX26 (888-546-8926) Fax: 503-716-3878 PO Box 25107 > www.GlobalLinuxSecurity.pro Linux since 1996! Portland, OR 97298 > -- 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