Before I address your question directly, let us return to AES-XTS, the cipher mentioned above.
Wikipedia says:
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XTS is supported by BestCrypt, dm-crypt, FreeOTFE, TrueCrypt, DiskCryptor, FreeBSD's geli, OpenBSD softraid disk encryption software, and Mac OS X Lion's FileVault 2.
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So both FreeBSD and OpenBSd use the same crypto primitive. Implementations differ, but with the same plaintext and the same keys, if the algorithm is deployed correctly and with the same options, both OSes should produce the same ciphertext.
The bits on the disk will be the same.
Now, to your question, which is multi-part. First, your password / passphrase / key:
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...when nobody do not have my pass...
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Because passwords and passphrases use text (ASCII or UTF-8), they are generally poor choices when used as keys. They can be attacked by "brute force" methods, or methods combined with "dictionary attacks". This weakness is inherent in human-readable / human-understandable keys. It is a separate issue from that of the the cipher that is used.
Both FreeBSD and OpenBSD offer password/passphrase options for generating keys that are used by the AES-XTS cipher. OpenBSD can use a key file (typically read from a USB stick) and while I have not checked FreeBSD's capabilities, I'm sure they offer something similar. A key file is not a password or a passphrase, but a fairly random collection of bits ... sometimes, thousands of bits long.
So the attacker can either attack keys, or attack the cipher itself. Passwords are easy to attack, passphrases can be attacked as well, they are just longer passwords.
Quote:
...can someone access to my data...
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I cannot answer whether AES-XTS is a "good" cipher, because I am not a cryptographer. And I've already mentioned that implementations may have weaknesses, even if the primitive does not. But regardless whether you choose FreeBSD or OpenBSD, the cipher itself should be the same. And, attacking the key is far, far easier than attacking the cipher. There is a famous cartoon about attacking the password when the cipher cannot be easily broken:
http://xkcd.com/538/
I hope this information has helped.