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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: 1 Mar 1996 22:19:30 GMT
Organization: Utah Valley State College, Orem, Utah
Lines: 37
Message-ID: <4h7t5i$qoh@park.uvsc.edu>
References: <4gejrb$ogj@floyd.sw.oz.au> <4gilab$97u@park.uvsc.edu> <4giqu8$aqk@park.uvsc.edu> <4gira2$a9d@park.uvsc.edu> <hpa.31321eee.I.use.Linux@freya.yggdrasil.com>
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Xref: euryale.cc.adfa.oz.au comp.unix.bsd.freebsd.misc:15417 comp.os.linux.development.system:19313
hpa@freya.yggdrasil.com (H. Peter Anvin) wrote:
] The problem is, sync metadata updates do *not* help you avoid losing
] data. It helps you from losing *files*. The two are not the same,
] since sync metadata doesn't help you make sure there is anything
] reasonable IN those files!
]
] Hence, given your last criterion, async metadata is better. It does
] what it claims to (work quickly), whereas sync metadata does not (help
] you avoid data loss).
I submit that not losing metadata is a prerequisite to not
losing data.
I further submit that files are container objects, and it is
optional whether or not the file system implements data
reliability as well (using journalling, logging, transaction
tracking, or some other as-yet-undiscovered techinque).
Now I agree that it is *also* optional whether the file system
guarantees metadata integrity (hence the -async option).
But I claim that without a guarantee of metadata integrity,
it's impossible to implement a system that guarantees data
integrity of data stored in a file system container object
(file).
Things like Informix skirt this issue by implementing the whole
file system in user space, which allows them to guarantee the
metadata integrity themselves. This works because they can
ensure metadata is committed to disk reliably before moving on.
Terry Lambert
terry@cs.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.