Honggang(Joseph) Yang <eagle.rtlinux@xxxxxxxxx> 于2019年10月12日周六 上午12:04写道：
Hi,
We implemented a new cache tier mode - local mode. In this mode, an
osd is configured to manage two data devices, one is fast device, one
is slow device. Hot objects are promoted from slow device to fast
device, and demoted from fast device to slow device when they become
cold.
I'm quite interesting about this and seems quite promising. But it seems objects level tier seems still not efficient enough in the small write scenario (4k ~ 8k based on your fio test result), right?
Now, in bluestore, it is possbile to implement a fine-grain local tier. it seems bluestore_pextent_t may be allocated from different devices and strategies like extent level hitset to evaluate whether some extents need to demote to slow devices. A promotion or demotion may submit a read with write operations in a transactions, and finished with a onode or blobs flushed into rocksdb.
The introduction of tier local mode in detail is
https://tracker.ceph.com/issues/42286
tier local mode: https://github.com/yanghonggang/ceph/commits/wip-tier-new
This work is based on ceph v12.2.5. I'm glad to port it to master
branch if needed.
Any advice and suggestions will be greatly appreciated.
thx,
Yang Honggang
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