> In regards to setting read ahead, how is this set for nvme drives? Also,
> below is our compression settings for the table… It’s the same as our tests
> that we are doing against SAS SSDs so I don’t think the compression
> settings would be the issue…
Check blockdev --report between the old and the new servers to see if there
is a difference. Are there other deltas in the disk layouts between the old
and new servers (ie. LVM, mdadm, etc.)?
You can control read ahead via 'blockdev --setra' or via poking the kernel:
In both cases, changes are instantaneous so you can do it on a canary and
monitor for effect.
Also, i'd be curious to know (since you have this benchmark setup) if you
got the degradation you are currently seeing if you set concurrent_reads
and concurrent_writes back to their defaults.
Apache Cassandra Consulting