Subject: Re: SOFTDEPS safe for qmail?
To: Jonathan Stone <jonathan@DSG.Stanford.EDU>
From: Andrew Gillham <gillhaa@ghost.whirlpool.com>
List: current-users
Date: 06/15/2000 22:15:14
Jonathan Stone writes:
> 
> Andrew,
> 
> Try reading it this way:
> 
> qmail uses the local filesystem as stable storage.  If the local
> filesystem guarantees that single-byte writes and directory operations
> are atomic, then qmail orders its writes such that will never lose
> mail except if the disk media itself dies.
> 
> Softdeps guarantee that the filesystem data and metadata is always
> _consistent_, but doesn't guarantee that the bits go all the way down
> out to disk synchronously at the point when the application issues
> system calls.  So a softdep system could crash and leeve the on-disk
> filesystem state consistent, but with qmail's "stable-storage"
> operations still buffered.   "Don't do that".
> 
> that's what I think they're trying to say.

Heh, sorry, didn't think about the data being written "safely" to
disk. :-)  I was assuming the warning was regarding metadata, but
I can see now it is probably related to the data itself.  This makes
make think Qmail's disk i/o would be slow if it is always syncing
the data.  Which might explain my sluggish mail server. :(

-Andrew
-- 
-----------------------------------------------------------------
Andrew Gillham                            | NetBSD ist Affengeil.
gillham@whirlpool.com                     | Nachts ist es kaelter
I speak for myself, not for my employer.  | als draussen.