Storage backend compatibility

Some storage backends do not support all the features of S3:

Atmos

does not return meaningful ETag
does not support multi-part upload
only supports object listing when delimiter is "/" -- does not support recursive listing
only supports object listing with prefixes when the prefix matches a directory name

limits container names to 63 characters and restricts character set to lowercase alphanumeric and dash
limits metadata keys to "C# identifiers". As far as I can tell, that's alphanumeric characters and dash; must not start with a number
does not support blob names with \ or with sequences of ./ and /.
maximum multipart upload size of 4.77 TB
does not support Expires header but does support Cache-Control header
does not support object-level access control
does not allow arbitrary list markers, partially emulated by mapping the last key to the opaque marker
does not return ETag as an MD5 hash, instead returning opaque data

bucket names must be between 6 and 50 characters and consistent of only letters, number, and hyphens
does not return ETag as an MD5 hash, instead returning SHA1 hash
does not support blob-level access control
does not support conditional GET
does not support copying objects
does not support Content-Disposition, Content-Encoding, Content-Language, Content-MD5, or Expiry headers
multipart upload requires at least 2 parts

does not allow arbitrary list markers, partially emulated by mapping the last key to the opaque marker
does not return ETag as an MD5 hash, instead returning opaque data
does not support listing in-progress multipart uploads
limits multi-part uploads to 32 parts