Cloud archive - rsync update doesn't work

With OVH Cloud Archive, how to rsync a folder, without RESEND the file each time ?

I tried many args possibilities (time, ...), but each time the content is resend.

Here example, with 2 txt files.

rsync --update -av "/mydir/" LOGIN_OVH@DOMAIN_OVH:DIR_OVH

sending incremental file list
[swift] GET *******/dstdir?format=json&limit=10000
[swift] GET -> 200
./
mail_2.txt
mail_cigale.txt
[swift] HEAD *******/dstdir/mail_2.txt
[swift] HEAD -> 200
[swift] PUT *******/dstdir/mail_2.txt [411610]
[swift] PUT -> 201
[swift] HEAD *******/dstdir/mail_cigale.txt
[swift] HEAD -> 200
[swift] PUT *******/dstdir/mail_cigale.txt [411610]
[swift] PUT -> 201


Thanks for help. I'm also open to alternatives solutions. My main purpose is only sync files of a folder.