On 12/28/2016 06:55 PM, Rick Stevens wrote:
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.
I did -- and the caching itself seems to be working just fine:
# lvs -o lv_name,vg_name,pool_lv,cache_read_hits,cache_read_misses
vg_raid10/lv_var
LV VG Pool CacheReadHits CacheReadMisses
lv_var vg_raid10 [lv_cache_pool_var] 96105 27540
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).
Appreciate the help.
Regards,
Raman