# @timestamp field in a datastream
**URL:** https://discuss.elastic.co/t/timestamp-field-in-a-datastream/252258
**Category:** Elasticsearch
**Created:** [October 15, 2020, 7:15pm UTC](https://discuss.elastic.co/t/timestamp-field-in-a-datastream/252258 "2020-10-15T19:15:41Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@MichaelKopaniov](https://discuss.elastic.co/u/MichaelKopaniov)
#### Post date: [October 15, 2020, 7:15pm UTC](https://discuss.elastic.co/t/timestamp-field-in-a-datastream/252258/1 "2020-10-15T19:15:41Z")
Hi,
I'm currently examining the migration of an old ES cluster into an ILM managed [https://www.elastic.co/guide/en/elasticsearch/reference/master/data-streams.html](https://datastreams).
I do not fully understand the role of the required @timestamp field.
I understand that writes are being directed to the write index while reads are being directed to all backing index. If writes are going to the current write index anyway, why does ES cares about the @timestamp field at all?
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### Author:  [@system](https://discuss.elastic.co/u/system)
#### Post date: [November 12, 2020, 7:15pm UTC](https://discuss.elastic.co/t/timestamp-field-in-a-datastream/252258/2 "2020-11-12T19:15:43Z")
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