On 12/28/2016 10:33 AM, Raman Gupta wrote: > I would like to change the cache mode of an existing lvm cache volume. > > I see the following in the man page: > > `With the --cachemode option, the cache mode can be set when creating > a cache LV, or changed on an existing cache LV.` > > However, it does not seem to work: > > # lvs -o cache_mode vg_raid10/lv_var > CacheMode > writethrough > # lvconvert --cachemode writeback vg_raid10/lv_var > # lvs -o cache_mode vg_raid10/lv_var > CacheMode > writethrough > > (Fedora 23, 4.8.14) > > The `lvconvert` command produces no output, and there is nothing in > dmesg or the journal. Have you tried adding the "-v" or "--verbose" flags to see if there is an issue?

On 12/28/2016 03:14 PM, Raman Gupta wrote: > On 12/28/2016 04:24 PM, Rick Stevens wrote: >> On 12/28/2016 10:33 AM, Raman Gupta wrote: >>> I would like to change the cache mode of an existing lvm cache volume. >>> >>> I see the following in the man page: >>> >>> `With the --cachemode option, the cache mode can be set when creating >>> a cache LV, or changed on an existing cache LV.` >>> >>> However, it does not seem to work: >>> >>> # lvs -o cache_mode vg_raid10/lv_var >>> CacheMode >>> writethrough >>> # lvconvert --cachemode writeback vg_raid10/lv_var >>> # lvs -o cache_mode vg_raid10/lv_var >>> CacheMode >>> writethrough >>> >>> (Fedora 23, 4.8.14) >>> >>> The `lvconvert` command produces no output, and there is nothing in >>> dmesg or the journal. >> >> Have you tried adding the "-v" or "--verbose" flags to see if there >> is an issue? > > No change: > > # lvconvert --verbose --cachemode writeback vg_raid10/lv_var > # lvs -o cache_mode vg_raid10/lv_var > CacheMode > writethrough Looking at the man page for lvconvert (at least under F24 and F25), the "--type cache" flag is necessary to specify the "--cachemode writeback" option: # lvconvert --verbose --type cache --cachemode writeback vg_raid10/lv_var You might have to specify the cache pool stuff as well. Not sure. I've never done this.

On 12/28/2016 03:46 PM, Raman Gupta wrote: > On 12/28/2016 06:35 PM, Rick Stevens wrote: >> On 12/28/2016 03:14 PM, Raman Gupta wrote: >>> On 12/28/2016 04:24 PM, Rick Stevens wrote: >>>> On 12/28/2016 10:33 AM, Raman Gupta wrote: >>>>> I would like to change the cache mode of an existing lvm cache volume. >>>>> >>>>> I see the following in the man page: >>>>> >>>>> `With the --cachemode option, the cache mode can be set when creating >>>>> a cache LV, or changed on an existing cache LV.` >>>>> >>>>> However, it does not seem to work: >>>>> >>>>> # lvs -o cache_mode vg_raid10/lv_var >>>>> CacheMode >>>>> writethrough >>>>> # lvconvert --cachemode writeback vg_raid10/lv_var >>>>> # lvs -o cache_mode vg_raid10/lv_var >>>>> CacheMode >>>>> writethrough >>>>> >>>>> (Fedora 23, 4.8.14) >>>>> >>>>> The `lvconvert` command produces no output, and there is nothing in >>>>> dmesg or the journal. >>>> >>>> Have you tried adding the "-v" or "--verbose" flags to see if there >>>> is an issue? >>> >>> No change: >>> >>> # lvconvert --verbose --cachemode writeback vg_raid10/lv_var >>> # lvs -o cache_mode vg_raid10/lv_var >>> CacheMode >>> writethrough >> >> Looking at the man page for lvconvert (at least under F24 and F25), the >> "--type cache" flag is necessary to specify the "--cachemode writeback" >> option: >> >> # lvconvert --verbose --type cache --cachemode writeback vg_raid10/lv_var >> >> You might have to specify the cache pool stuff as well. Not sure. I've >> never done this. > > Yup, that's what I tried in the first place, but that doesn't work either: > > # lvconvert --verbose --type cache --cachemode writeback vg_raid10/lv_var > --cache requires --cachepool. > Run `lvconvert --help' for more information. > > Ok fine: > > # lvconvert --verbose --type cache --cachepool > vg_raid10/lv_cache_pool_var --cachemode writeback vg_raid10/lv_var > Executing: /usr/sbin/modprobe dm-cache-mq > Executing: /usr/sbin/modprobe dm-cache-smq > Cache is not supported with cache segment type of the original > logical volume vg_raid10/lv_var. > > Argh. Did you follow the examples in "man lvmcache" when you set this up? Something isn't right with the way the cache pool is set up.

As I said, I've never done LVM cache stuff. I'd have to tinker with it at home tonight (not risking my production machines here at the office).