QMail and SoftUpdates

Xin LI delphij at frontfree.net
Mon May 17 10:49:35 PDT 2004

On Mon, May 17, 2004 at 01:18:15PM -0400, Mikhail Teterin wrote:
> The link at
> 	http://cr.yp.to/qmail/faq/reliability.html#filesystems
> claims, using SoftUpdates for mailqueue is dangerous. Is that still
> true? Thanks!

Yes, it is dangerous. Same is true for any journalling file systems,
which essentially does the same thing: delayed write of data/metadata.

Delayed write will make it possible for the Operating System to group
several writes together and write them once, or at least, in a better
order in order to improve performance. However, for the mail case, once
it responds "250", then the remote peer is allowed to remove the message
from its queue. If the system crashes, and the data was not written into
disk, then your message is lost.

Mounting your mailqueue slice with -noatime is a good idea, too.

Please note that disabling SoftUpdates will drastically decrease write
performance on that slice. Of course, if your system often encounter
crash or power failure, it will be a good idea to disable it.

Xin LI <delphij frontfree net>	http://www.delphij.net/
See complete headers for GPG key and other information.

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