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From: Terry Lambert <terry@lambert.org>
Newsgroups: comp.unix.bsd.freebsd.misc,comp.os.linux.development.system
Subject: Re: The better (more suitable)Unix?? FreeBSD or Linux
Date: 13 Feb 1996 01:49:25 GMT
Organization: Utah Valley State College, Orem, Utah
Lines: 37
Message-ID: <4foqn5$art@park.uvsc.edu>
References: <4er9hp$5ng@orb.direct.ca> <4fl488$oqi@kogwy.cc.keio.ac.jp>
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hosokawa@mt.cs.keio.ac.jp (HOSOKAWA Tatsumi) wrote:
] I have two questions about this sync/async problems (I don't have
] detailed knowledge about filesystem).
]
] If the 'sync' operation on async filesystem is done in order of the
] original write requests was issued, it's safe. But I think it reduces
] the performance of filesystem.
It is, and it does.
The intent is to order metadata writes. The implementation is
via synchronous operation.
] If it is done in unordered fashion, I think it causes the same (but
] more critical) problems on async filesystem. Is it wrong?
Yes, async updates of metadata without another mechanism to
satisfy the ordering requirements of deterministic recoverability
is far more dangerous than sync.
] BTW, I've used BSD filesystem for years, I haven't see the dead file's
] garbage appeared as another file even after severe crashes (I'm a
] device driver writer of FreeBSD and I frequently experience unclean
] shutdowns). I've thought that these premature files are truncated by
] fsck. Is it wrong?
No, you are right. The block allocation map/bitmap is also updated
synchrnously. The idea that a file could contain bogus data that
belonged to another (sensitive) file is nothing more than a red
herring (ie: something intended to introduce uncertainty).
Terry Lambert
terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.