scattered read and sequential read

Scattered Read - normally attributable to full table scans. These wait events occur through full table scans (FTS) as FTS normally scan multiple blocks at the same time, re: multi_block_read_count.

Sequential Read - read 1 block at a time are normally attributable to index scans. As index scans read 1 block at a time, multi block read doesn't apply with indexes and performance with sequetial reads could go down.

If any of these events are high then ensure stats are accurate, explain plans look OK and there isn't too much disk contention going on.

note: The amount of blocks that an index has to scan through before completing could have a big impact on performance. This also has implications for the cluster factor.