[linux-lvm] Two questions about lvm-cache
Raman Gupta
rocketraman at gmail.com
Thu Dec 29 13:52:24 UTC 2016
I am trying out the lvmcache functionality. So far, everything looks
great. I have two questions:
1) The man page of lvmcache states "With the --cachemode option, the
cache mode can be set when creating a cache LV, or changed on an
existing cache LV." However, I can't figure out the right command to
change the cache mode on an existing LV.
# lvs -a -o +devices
(see https://paste.fedoraproject.org/514698/83019352/raw/)
# lvs -o cache_mode vg_raid10/lv_var
CacheMode
writethrough
# lvconvert --verbose --cachemode writeback vg_raid10/lv_var
(no output)
# lvs -o cache_mode vg_raid10/lv_var
CacheMode
writethrough
# 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.
2) Does lvm manage TRIM on the cache device? Normally I set up SSD
volumes with a weekly fstrim, but that only works for mounted filesystems.
Thanks!
Raman
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