xtrabackup using stream

I’m new to percona xtrabackup and I’ve been trying to perform a full backup stream from my local ( test server around 600GB ) to remote server.
I just have some questions and I need guides, and I think this is the best place .

I have this command which I executed in my local
innobackupex --user=user --password=password --stream=tar /which/directory/ | pigz | ssh user@10.11.12.13 “cat - > /mybackup/backup.tar.gz”

My questions are :
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[*]My log scan is not changing / increasing
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log scanned up to (270477048535)
log scanned up to (270477048535)
log scanned up to (270477048535)
log scanned up to (270477048535)
log scanned up to (270477048535)

I’ve read a comment before and someone says log scan will not increase if no one is using the database. ( Yes, no one is using the database )
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[]It’s been running for a while.
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I’ve tried to use xtrabackup to a local test server with around 1.7TB and finished in just a few hours. Is this because I’m using stream that’s why it is slow ?
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[
]What is the purpose of "/which/directory/" in my command? Is it going to store the file in /which/directory/ first and then transfer to my remote server ? Why do I have to specify a directory?
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[*]No created file on my local server /which/directory/ and to my remote server /mybackup/.
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Am I doing something wrong ? Is there a much easier way to perform this?
My only goal is to backup my local database to a remote server, I’m doing this stream because I don’t have enough disk space to store my backup locally.

I’m using MariaDB 5.5 and Percona xtrabackup 2.2

Can anyone help me ? Thanks in advance .