Re: journaling filesystem

Peter Svensson (
Thu, 14 May 1998 14:39:15 +0200 (MET DST)

On Thu, 14 May 1998, Hans Reiser wrote:

> Do we need to order writes, or do we need to merely know when a write
> has completed, and let the FS order the writes?

That depends on how the filesystem is implemented and what guarantees it
wants to give the user. A journaling filesystem needs neither, if one
accepts that the filesystem may return to a state it was several seconds
before a crash (really the last point in time for which the journal is
complete). This is possible if the disk subsystem guarantees a certain
maximum age a request can reach while sitting in the write cache.

When dealing with network clients one usually wants to know when the data
has actually hit the platters, as is the case for mailservers. There
usually is a tradeoff between what guarantees can be given and the


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