Some files must be kept even though nobody expects to open them soon. The Azure Blob Storage archive tier is for those files: large backups, original raw data, and records retained for legal requirements. It has the lowest storage cost of the hot, cool, and archive tiers, but it is offline. A file must be rehydrated before retrieval, which can take hours and incurs higher access costs. section 5.3.1 section 5.8 section 9.5.1
Choose the tier by how soon data must be available, not just by its storage price. Hot suits files needed immediately; cool suits infrequently accessed files that still need reasonable retrieval times. Archive suits rarely accessed data whose retrieval can wait. A cheap place to keep a file is less helpful if customers need it right now. section 5.3.1 section 5.8
Let older blobs move on their own
A lifecycle policy can move a block blob to cool after 30 days without modification, then to archive after 90 days, and delete it after 365 days. Save the JSON policy as policy.json and create the storage-account management policy with the Azure CLI. Check that those timings fit how long the data must remain available and how long it must be kept. section 9.5.1
{
"rules": [
{
"name": "TransitionHotToColdToArchive",
"enabled": true,
"type": "Lifecycle",
"definition": {
"actions": {
"baseBlob": {
"tierToCool": {
"daysAfterModificationGreaterThan": 30
},
"tierToArchive": {
"daysAfterModificationGreaterThan": 90
},
"delete": {
"daysAfterModificationGreaterThan": 365
}
}
},
"filters": {
"blobTypes": [
"blockBlob"
]
}
}
}
]
}
The JSON listing shows the modification-age thresholds, blob-type filter, and actions for moving blobs to cool and archive before deletion. section 9.5.1
C:/> az storage account management-policy create --account-name banningstorage --resource-group BanningRG --policy @policy.json
The CLI listing shows how to apply policy.json to a storage account. section 9.5.1
