How to: Change LVM Cache / dm-cache mode

LVM2 has a built in cache feature to use slow disk with SSDs. Although, by default, it changes the cache to use Writethrough. If you have a battery backed unit with RAIDed SSDs, you may want to use Writeback cache mode to achive faster write performance. 

To find current cache mode, you can run the following on the cached pool:

# lvs -o+cache_mode vg0_727b_121217/vpsextra
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert CacheMode
vpsextra vg0_727b_121217 Cwi-aoC--- 3.00t [cache] [vpsextra_corig] 5.45 0.73 0.00 writethrough


To change the CacheMode to Writeback, use the following:

# lvchange --cachemode writeback vg0_727b_121217/vpsextra
Logical volume vg0_727b_121217/vpsextra changed.

Check the current CacheMode:

# lvs -o+cache_mode vg0_727b_121217/vpsextra
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert CacheMode
vpsextra vg0_727b_121217 Cwi-aoC--- 3.00t [cache] [vpsextra_corig] 5.48 1.08 0.07 writeback

  • lvm cache, dm-cache, ssd cache, lvm, centos
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