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Re: ext3 and chattr +S on postfix spools



Erik Smit:
> On Tue, 2002-02-05 at 04:20, Wietse Venema wrote:
> > ext3 is unsafe for maildir, and with softupdates, so is ffs.
> > One step forwards, two steps back.
> > 
> > Fortunately, some people still have a choice.
> 
> For the newbies among us (me :) would you mind explaining what exactly
> causes it to be unsafe? As far I know (but like I said, I'm just a noob)
> ext3 is journalling metadata and data so I cannot understand how data
> could be lost.

maildir delivery requires that certain file system operations are
atomic and synchronous.

Atomic, to prevent multiple processes from corrupting each other's
result.  This eliminates the need for application-level locking,
which is necessary with traditional UNIX-style mailboxes.

Synchronous, so that the process has certainty whether or not an
operation completed successfully, which is necessary for reliable
mail delivery. maildir expects that the link and unlink operations
are completed when the system call returns.

Translated into ext3 speak that means: the link and unlink operations
are written to the log before the respective system call returns.

	Wietse





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