What happens to a file in Azure Storage V2 after 30 days in cool tier and 180 days in archive tier?
But according to what I understand from above link, file will be deleted from cool tier after 30 days and from archive tire after 180 days.
No, Microsoft will definitely not automagically delete your data, if your subscription is in good standing. They want you to store as much data for as long as possible - it's more profitable for them :) (Although note that there is an explicit Blob Lifecycle Management feature in the works)
What MS mean by this is that Cool and Archive storage is cost-optimized for a period of at least 30 and 180 days, respectively. In essence, you'll be 'penalized' for deleting data before 30 / 180 days by paying in the same amount as if you had left the file there for 30 or 180 days.
If you scan the pricing pages for block blobs
Cool and Archive early deletion In addition to the per-GB, per-month charge, any blob that is moved to Archive is subject to an Archive early deletion period of 180 days. Additionally, for General Purpose v2 accounts, any blob that is moved to Cool is subject to a Cool early deletion period of 30 days. This charge is prorated. For example, if a blob is moved to Archive and then deleted or moved to the Hot tier after 45 days, the customer is charged an early deletion fee equivalent to 135 (180 minus 45) days of storing that blob in Archive.
FWIW my 10 cents:
Hot Tier - You pay a bit more (~20%) to store the data per GB per month, but you can store it for as short a period as you like, and you aren't charged bandwidth to retrieve the data. A common use case here would be for user-uploaded data which would typically be shared or published and frequently read.
Cold Tier - slightly cheaper storage per GB per month, but retrieval isn't free. The use case here would be for data which you don't necessarily expect to read frequently, such as log data, or short term backups, but if you do need to read it, it's still quick to get to the data.
The read and write performance of hot and cold should be similar
If in doubt, I would start with hot, and then only once I understood the typical lifespan and access needs to my data would I start changing things up.
Premium Tier - Stored on SSD's - storage will cost considerably more, but performance will be better. For small files which need to be retrieved quickly, I would also consider looking at a secondary caching tech like Azure Redis Cache - that way you can persist data in cheaper hot storage, and cache in Redis.
Archive Tier - Although the storage is insanely cheap, it should be regarded as offline. You'll pay a hefty $5 fee for your first 10k read operations from Archive, and the SLA on read latency is several hours. Use cases for Archive could be for old backup archives, or bulk storage for corporate governance or statutory reasons (e.g. 5 year's worth of financial records), i.e. data which you hope to never need again, but will gladly pay for if you do.