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.
Regards,
Raman
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