I am trying to use zram for the dmcache meta and dmcache caching device to cache a local logical volume. It works just fine if I use logical volumes from a disk as the caching device, but using a zram block device as the cache sets up properly but fails to boot a virtual machine on the resulting volume. Interestingly, I can use zram as a meta cache device without error, but using zram as the cache itself is when this fails. This is how I'm setting up my device map: 0 20758528 cache /dev/zram0 /dev/zram1 /dev/c0v0/vdb 64 1 writethrough mq 6 sequential_threshold 5120 random_threshold 2 migration_threshold 819200 zram0 and zram1 are both 1GB in size so plenty of space here. I am booting linux 3.11.4 with that version of dmcache. When I try and boot a VM off of the resulting cache, the VM fails to write to it's disk (I think), and displays the following error when booting CentOS 6: mount: wrong fs type, bad option, bad superblock on /dev/mapper/VM_NAME, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so Kernel Panic - not syncing: Attempting to kill init! Pid: 1, comm: init Not tainted 2.6.32-279.e16.x86_64 #1 Call Trace: [<ffffffff814fd11a>] ? panic+0xa0/0x168 [<ffffffff81070bd2>] ? do_exit+0x862/0x870 [<ffffffff8117ca75>] ? fput+0x25/0x30 [<ffffffff81070c38>] ? do_group_exit+0x58/0xd0 [<ffffffff81070cc7>] ? sys_exit_group+0x17/0x20 [<ffffffff8100b0f2>] ? system_call_fastpath+0x16/0x1b Can you think of any reason that zram cannot be a cache for dmcache devices? If this is a bug, does it reside in dmcache or in zram? How can I test this further? -Daniel -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
