Hi all, I have configured a ceph cluster to be used as an object store with a 
combination of SSDs and HDDs, where the block.db is stored on LVM on SSDs and 
the OSD block is stored on HDDs. 
I have set up one SSD for storing metadata (rocksDB), and five HDDs are 
associated with it to store the OSD blocks. 
During a disk replacement test, if one SSD that stores the block.db fails, all 
five associated OSDs go down. 
When replacing and recovering the failed SSD, it seems necessary to reconfigure 
the five OSDs, which takes too long to recover data and has significant 
performance impact. 
So here are two questions:

- Is it common practice to configure SSDs with block.db and associate them with 
five HDD disks to store OSD blocks when using eight SSDs and forty HDDs? 
  Or would it be better to only store the rgw index on SSDs? I am also curious 
about the difference in performance between these configurations.
- If SSDs are configured with block.db as described above, will it be necessary 
to reinstall the five associated OSDs (HDDs) if one SSD fails ? 
  Also, is there a way to reconstruct the metadata on the newly replaced SSD 
from the remaining five intact HDDs? 

As a novice in ceph clusters, I seek advice from experienced users. 
Thank you.
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