Some people simply trust more mature DBs or HDFS more than ES or feel more
comfortable with them. At the same time, others rely on just ES to hold
their data. If you trust the hardware you run ES on, if you have high
enough replication level, if you trust your team's ability to upgrade ES
smoothly, etc. then you could use just ES. One thing ES doesn't have
worked out well yet is backup, which may be important to you.
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