> 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:
/sys/block/[YOUR DRIVE]/queue/read_ahead_kb

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.

Nate McCall
Wellington, NZ

Apache Cassandra Consulting

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