Mention 'disk i/o optimized' mode should be used with Magma buckets

For Magma buckets, the 'writer thread settings' as described in https://docs.couchbase.com/server/current/manage/manage-settings/general-settings.html#data-settings should be set to 'Disk i/o optimized' in order to get best performance.

This is what I suggest:

On the https://docs.couchbase.com/server/current/learn/buckets-memory-and-storage/storage-engines.html#storage-engine-magma page, add the following para:

"In order to get maximum performance from Magma for disk-oriented workloads, it is recommended to set the Writer Threads to 'Disk i/o optimized' (refer to the Data Settings page here). This setting will ensure there are enough threads to sustain high write rates. "

Alternatively (or maybe additionally) mention the same para in the https://docs.couchbase.com/server/current/manage/manage-settings/general-settings.html#data-settings page also.

I recommend adding this text to both the pages.