From: "Stephen C. Tweedie" <sct@redhat.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: Oron Ogdan <Orono@m-sys.com>, MTD list <mtd@imladris.mvhi.com>,
Stephen Tweedie <sct@redhat.com>
Subject: Re: Power Down
Date: Fri, 10 Dec 1999 10:41:45 +0000 (GMT) [thread overview]
Message-ID: <14416.55529.249995.920763@dukat.scot.redhat.com> (raw)
In-Reply-To: <E11vdnY-0002hW-00@devel2.axiom.internal>
Hi,
On Wed, 08 Dec 1999 09:54:12 +0000, David Woodhouse
<dwmw2@infradead.org> said:
> Orono@m-sys.com said:
>> The only way to be resistant to power failures in the file system
>> level is to use a log-structured file system.
>> I heard ext3 is log-structured but I am sure one of the Linux guys here
>> knows more about this,
> ext3 is a journalling filesystem. I believe that it's not log-structured.
Correct.
> Journalling is sufficient for protection from power failures. Stephen,
> would you care to elaborate on the difference?
Log-structured disks are, oddly enough, structured as a log! The
entire data layout is in the form of a conceptually infinite log. All
disk writes are performed at the head of the log, so writes are
necessarily sequential. The write performance, as a result, is
unmatched. The read performance can sometimes suffer, but these
filesystems are intended for use with huge amounts of cache, so that
the write performance is more important: most reads are from cache.
A journaled filesystem has a log *in addition to* the normal disk
structure. The log is used for recovery after a crash but does not
store any long-term persistent data for the filesystem.
> I believe that NTFS is also journalling but not log-structured.
Indeed.
Cheers,
Stephen
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next prev parent reply other threads:[~1999-12-10 10:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-12-08 0:58 Power Down Oron Ogdan
1999-12-08 9:54 ` David Woodhouse
1999-12-10 10:41 ` Stephen C. Tweedie [this message]
-- strict thread matches above, loose matches on Subject: below --
1999-12-08 14:55 Bob Canup
1999-12-08 15:04 ` David Woodhouse
1999-12-08 8:57 Oron Ogdan
1999-12-03 19:28 power down Bob Canup
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