In the last recipe, we created a pool, cache-pool, based on SSDs. We will now use this pool as a cache tier for the erasure-coded pool, EC-pool, that we created earlier in this chapter:
The following instructions will guide you through the creation of a cache tier with the writeback mode and setting the overlay with an EC-pool:
- Create a cache tier that will associate storage-pools with cache-pools. The syntax is:
ceph osd tier add <storage_pool> <cache_pool>:# ceph osd tier add EC-pool cache-pool - Set the cache mode as either
writebackorread-only. In this demonstration, we will usewriteback, and the syntax is:ceph osd tier cachemode <cache_pool> writeback:# ceph osd tier cache-mode cache-pool writeback - To direct all the client requests from the standard pool to the cache pool, set the pool overlay using the syntax:
ceph osd tier set-overlay <storage_pool> <cache_pool>:# ceph osd tier set-overlay EC-pool cache-pool
- On checking the pool details, you will notice that the
EC-poolhastier,read_tier, andwrite_tierset as48, which is the pool ID for thecache-pool. Similarly, forcache-pool, the settings will be:tier_ofset to47andcache_modeaswriteback. All these settings imply that the cache pool is configured correctly:# ceph osd dump | egrep -i "EC-pool|cache-pool"
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