On Wed, Jan 23, 2013 at 08:37:10PM +0800, Nitin Kshirsagar wrote: > Hello Kent, > > I have setup bcache and run fio data verification test on write back and write through caches. > The fio tests are passed, however I have found following issues while using bcache. > > Issue1: Cache is not created as per user specified options > -------------------------------------------------------------------------------------------------------- > Steps: > 1.Create cache by specifying mode writeback and cache replacement policy as fifo > [root@annu bcache]# make-bcache --cache /dev/sdc --bdev /dev/sdd --writeback --cache_replacement_policy=fifo > UUID: e25f2840-f02b-46af-81e7-28948b2737cc > Set UUID: 68da5b89-1e87-457a-80c7-2c822737f969 > nbuckets: 2048 > block_size: 1 > bucket_size: 1024 > nr_in_set: 1 > nr_this_dev: 0 > first_bucket: 1 > UUID: a3ce52e6-631b-4c74-afa2-9f8b0088c7f4 > Set UUID: 68da5b89-1e87-457a-80c7-2c822737f969 > nbuckets: 20480 > block_size: 1 > bucket_size: 1024 > nr_in_set: 1 > nr_this_dev: 0 > first_bucket: 1 > > [root@annu bcache]# echo /dev/sdc > /sys/fs/bcache/register > [root@annu bcache]# echo /dev/sdd > /sys/fs/bcache/register > > > 2. Cache mode should be "writeback" instead of "writethrough" > [root@annu bcache]# cat /sys/block/bcache2/bcache/cache_mode > [writethrough] writeback writearound none > [root@annu bcache]# cat /sys/block/bcache2/bcache/writeback_running > 1 > > 3. Cache policy should be "fifo" instead of "lru" > [root@annu ~]# cat /sys/block/bcache2/bcache/cache/cache0/cache_replacement_policy > [lru] fifo random These two are... oddities/documentation bugs with make-bcache. Options apply to devices you specify _after_ the option, not before - it was implemented this way so you could format cache devices and backing devices at the same time - and really, the other options should be parsed differently but I haven't spent much time on make-bcache. Patches welcome :) > Issue2: Cache dirty data value should not be negative. > ------------------------------------------------------------------------------------------------------- > Steps: > > 1.Create cache by specifying mode writeback and cache replacement policy as fifo > 2.To make bcache devices known to the kernel > [root@annu bcache]# echo /dev/sdc > /sys/fs/bcache/register > [root@annu bcache]# echo /dev/sdd > /sys/fs/bcache/register > 3.Create FS on cache /dev/bcacheN and mount in directory > 4.Create Data set by using fio or dd on mount point. > 5. Change cache node from "writethrough" to "writeback" > [root@annu ~]# echo writeback > /sys/block/bcache2/bcache/cache_mode > [root@annu ~]# cat /sys/block/bcache2/bcache/cache_mode > writethrough [writeback] writearound none > 6.Check cache dirty data should not be negative value > [root@annu ~]# cat /sys/block/bcache2/bcache/dirty_data > -9.4M Known bug, but fairly harmless one. That value is only used for the pd controller that adjusts the background writeback rate - and in practice when there's dirty data in the cache it shouldn't be _too_ far off. It's on the todo list, but it'll be a bit before I get to it. -- 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
