Date: Fri, 17 Dec 1999 02:53:29 +0100 (CET) From: Oliver Fromme <olli@dorifer.heim3.tu-clausthal.de> To: freebsd-questions@FreeBSD.ORG Subject: Re: softupdates cont'd... Message-ID: <199912170153.CAA11742@dorifer.heim3.tu-clausthal.de>
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Jonathon McKitrick wrote in list.freebsd-questions:
> Well, softupdates are up and running for real this time ;-)
> Has anyone found any limitations, or circumstances when they are
> undesirable? As i understand it, the negatives are minimal:
>
> 1. More memory is used
This is true.
> 2. The FS _may_ be prone to corruption in rare circumstances
Haven't experienced that (and we're using soft-updates on a lot
of boxes, some of which are under quite some load). However,
there are two points to consider:
- When files are revode, their space is not marked as free
immediately, but after some "sync period" when the metadata
is written back to disk. This can be up to 30 seconds (you
can watch this with "df").
This can be a problem when you do a "make installword", for
instance, and your root filesystem doesn't have enough space
to hold twice the stuff in /bin and /sbin -- It will just
run out of space, and you could end up without having a
/bin/sh anymore or something like that, which is a bad thing,
of course.
Even worse, there have been reports that the system could
crash (panic) if the space on a soft-updates-enabled file-
system overflowed. I don't know if this problem has been
fixed (never happened to me anyway).
For the above reasons, it is in general recommended _not_ to
enable soft-updates on your root filesystem. It wouldn't
help much anyway, because there are usually not many write
accesses to that filesystem (provided that you have /var and
/tmp separately, of course, which is always a good idea).
Mounting / with the noatime option is usually enough, or even
read-only if you don't mind re-mounting it each time you have
to change something in /etc.
- When soft-updates is enabled and the system crashes (e.g by
a power failure or a kernel panic), you will lose files which
have been re-written within the past 30 seconds (they will be
there, but the size will be zero). Without soft-updates,
there usually is still some content left from such files.
> Has anyone found the system sluggish during makes (more than without
> softupdates) or otherwise limited during some particular activity?
I experience such slugginess once on an IDE-only system without
UDMA enabled (but with soft-updates). Enabling UDMA in the wdc
driver fixed it.
Regards
Oliver
--
Oliver Fromme, Leibnizstr. 18/61, 38678 Clausthal, Germany
(Info: finger userinfo:olli@dorifer.heim3.tu-clausthal.de)
"In jedem Stück Kohle wartet ein Diamant auf seine Geburt"
(Terry Pratchett)
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