Improving KVM performance with BCACHE

Quags

Administrator
Staff member
I've been testing around bcache for our KVM windows servers. Bcache ( http://bcache.evilpiepirate.org/ ) is now in the 3.10 kernel and can use a ssd drive to cache data over a normal sata/spinner drive. So far it is looking great. Over 6 days, with 13 windows vms:

Code:
==> /sys/block/bcache0/bcache/stats_total/bypassed <==
31.6G

==> /sys/block/bcache0/bcache/stats_total/cache_bypass_hits <==
16076096

==> /sys/block/bcache0/bcache/stats_total/cache_bypass_misses <==
0

==> /sys/block/bcache0/bcache/stats_total/cache_hit_ratio <==
87

==> /sys/block/bcache0/bcache/stats_total/cache_hits <==
9286482

==> /sys/block/bcache0/bcache/stats_total/cache_miss_collisions <==
11368

==> /sys/block/bcache0/bcache/stats_total/cache_misses <==
1386327

==> /sys/block/bcache0/bcache/stats_total/cache_readaheads <==
0
and 87% cache_hit_ratio. Only read cache is enabled. There is a way to cache writing as well, I do not recommend enabling it if you care about your data.

Currently running on Ubuntu 14.04 LTS

Assuming all goes well, I expect all newer KVM servers will be using bcache. More info on bcache is at http://www.linux.com/learn/tutorials/754674-using-bcache-to-soup-up-your-sata-drive
 
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